: New Zealand's second largest city has been hit by a strong earthquake, measuring 6.3 in magnitude, with first reports suggesting there are multiple fatalities and people trapped in buildings. This is the second earthquake in five months to hit the region, with a 7.1 magnitude quake in September last year which caused widespread damage but there were no deaths. You can follow a live-feed of the rescue here and read our latest news story on what happened when the quake hit.
Here are some of the latest details coming through from Reuters.
A strong quake hit New Zealand's second-biggest city of Christchurch, toppling buildings, causing "multiple fatalities", trapping people beneath rubble and sparking fires.
Local TV showed bodies being pulled out of rubble strewn around the city centre, though it was unclear whether any of them were alive, but police reported multiple fatalities after the 6.3 magnitude quake struck during the busy lunchtime.
"I was in the square right outside the cathedral - the whole front has fallen down and there were people running from there - there were people inside as well," said John Gurr, a camera technician who was in the centre of the city when the quake hit.
"A lady grabbed hold of me to stop falling over ... It's not nice at all. We just got blown apart. Colombo Street, the main street, is just a mess ... There's lots of water everywhere, pouring out of the ground - its liquefaction - its an absolute mess."
New Zealand Prime Minister John Key is on his way to Christchurch following an emergency cabinet meeting in Wellington. Earlier he told cabinet:
This is a very populated time with people at work and children at school. Sadly, I cannot rule out whether there have been fatalities or not. But we are aware of significant damage to buildings that had people in them at the time."
There are numerous reports of people trapped in buildings throughout the city though details remain unclear as to numbers.
It is huge. We just don't know if there are people under this rubble," a priest standing outside the rubble of a damaged cathedral told New Zealand television.
You can follow a live-stream of the rescue effort taking place in Christchurch here.
Christchurch mayor Bob Parker has given an interview to Radio New Zealand:
We now need to think about all the things we learnt at that time (of the September 4 quake). Emergency services now have the incredibly difficult task of navigating a city which is evacuating itself. We need to start the process of checking hundreds of people. I don't have an overview. That was as violent as the earthquake we had on the September 4th. We had a nasty shock again about 30 to 60 seconds later."
TV3 New Zealand is reporting that the city has run out of ambulances and Christchurch airport is closed to all but emergency flights. Police have said there was a report of two buses crushed under falling buildings. Power and telephone lines were knocked out, and pipes have burst, flooding the streets with water.
It appears that the timing of the quake - when the city was at its busiest with many people moving around during their lunch hour, has meant that while it was of less magnitude than the earthquake in September last year, the damage has been far more extensive, and injuries worse. Witnesses have said the gravity of the force felt a lot stronger than 6.3. The US Geological Survey said the quake struck near the city with a shallow depth of 4 kilometres, shortly before 12:50pm local time.
Christchurch mayor Bob Parker has declared a level 3 emergency in Christchurch and the city is being evacuated. "Make no mistake this is going to be a very black day for this shaken city," he said when asked about possible deaths.
The Pyne Gould Guinness Building, a multi-story structure housing more than 200 workers, has collapsed and an unknown number of people are trapped inside.
The cathedral of Christchurch, New Zealand, on December 13, 2010, South Island. Photograph: Eyeswideopen/Getty Images
One of the buildings which appears to have some of the worst damage so far is the Christchurch Cathedral, a site of much affection throughout the city. Here are pictures showing the damage. This is am image of the Cathedral taken at the end of last year.
An exterior view shows the remains of Christchurch's cathedral after an earthquake in Christchurch, New Zealand, in this February 22, 2011 Photograph: Reuters Tv/REUTERS
Here is an image as the earthquake hit where you can see some of the damage done to the Catherdral.
Some of the descriptions coming through from witnesses can give us a little bit more of a picture about what happened when the quake struck. Gary Moore said he and 19 other colleagues were trapped in their twelfth floor office after the stairwell collapsed in the quake. He did not know if people on other floors were trapped.
We watched the cathedral collapse out our window while we were holding onto the walls. Every aftershock sends us rushing under the desks. It's very unnerving but we can clearly see there are other priorities out the window. There has been a lot of damage and I guess people are attending to that before they come and get us.
City councilman Barry Corbett, who was on one of the top floors of the city council building when the quake struck.
When the shaking had stopped I looked out of the window, which gives a great view onto Christchurch, and there was just dust. It was evident straight away that a lot of buildings had gone.
John Gurr, a camera technician who was in the city centre when the quake hit said:
I was in the square right outside the cathedral - the whole front has fallen down and there were people running from there. There were people inside as well. A lady grabbed hold of me to stop falling over...We just got blown apart. Colombo Street, the main street, is just a mess...There's lots of water everywhere, pouring out of the ground.
The New Zealand Herald has spoken to Kevin Fenaughty, the data centre manager at Geonet, who said the epicentre of the quake was located at the "worst possible location" for the city.
It's a nightmare. A lot of people were just getting back on their feet after the original quake.
I'm going to handover to my colleague - and former resident of New Zealand, Richard Adams to take over for a little while.
Thanks Lee. As a former resident of Canterbury I know the city well and I have many relatives and friends living there, and the live footage being shown on television is devastating.
Here's an summary of how things stand at the moment:
• Just before 1pm local time the city of Christchurch was hit by a major earthquake registering 6.3 on the Richter scale, close to the surface, making it more damaging than the 7.1 scale shock that hit the city in September
• Police and civil defence authorities have confirmed that there are an unknown number of casualties but warn of "major" tragedy
• Two commuter buses were crushed under falling debris
• City authorities have ordered the evacuation of the city centre, as after-shocks threaten weakened buildings, power and water has been cut off and sewerage pipes have ruptured
• A major search and rescue operation is under way to find people trapped inside collapsed buildings in the centre of the city, with at least 30 thought to be in one building alone and perhaps several hundred overall
• The steeple of Christchurch Cathedral, a city landmark, has partly collapsed with reports of people trapped inside the cathedral
• The New Zealand dollar's value has tumbled on foreign exchanges
National broadcaster TVNZ has opened a live web feed for international viewers to watch events in Christchurch here.
Radio New Zealand's National programme is running rolling news with a live audio feed here.
The local newspaper is the Christchurch Press, and its office is right on Cathedral Square in the city centre – and it has posted this chilling video footage of the immediate aftermath. It's like a horror film.
Warning: contains distressing scenes
It's clear that the devastation is far worse than the earthquake in September.
Most of the attention has focussed on the city centre but news is filtering in from the nearby port of Lyttelton and seaside town of New Brighton, both closer to the centre of the earthquake. Now TV3 channel is reporting that the two towns are "unliveable", which suggests considerable damage.
Google has launched an online people finder service for victims of the Christchurch earthquake.
The Canterbury Television building has been one of the hardest hit in the centre of the city, with several bodies being taken out on stretchers and parts of the building on fire. Burst water mains in the area means that fire fighters are having to use monsoon buckets to put it out.
The New Zealand Herald has the most grim news so far, of "bodies lying in the streets" of Christchurch:
Residents are reporting bodies lying in the streets of Christchurch following this afternoon's magnitude 6.3 earthquake.
Police said fatalities had been reported at several locations and that two buses had been crushed by falling buildings. Christchurch mayor Bob Parker has declared a state of emergency.
Christchurch resident Jaydn Katene told the Herald: "We've had friends in town call us and say there are just bodies lying around; lots of dead bodies outside shops just lying there just covered in bricks."
The mayor of Christchurch, Bob Parker, has just given a press conference in which he has tried to prepare the city for a "major tragedy".
At least 17 people have been confirmed dead. Authorities are warning to expect more. #NZeq
John Bergin
theburgerman
It now seems the death toll will be far higher than feared, based on this news from John Bergin, director of digital news for Sky News Australia.
The New Zealand prime minister John Key has now confirmed that 65 people are dead. This is surely the worst tragedy in New Zealand since the 1977 Erebus air disaster.
Prime minister John Key is now on Radio New Zealand, saying: "This may be New Zealand's darkest day".
Key says that it's hard to know how many people are still trapped – and casually mentions that the building behind him in Latimer Square is on fire.
He confirms that the figure of 65 dead is based on bodies that have been removed from buildings – and implies that there could be more to come.
On top of the Pike River mine disaster in November last year – in which 29 people died – and the earlier earthquake in September it has not been a happy few months for New Zealand's South Island.
Here is dramatic footage from the air, taken by helicopter, showing the full extent of the devastation in Christchurch.
Toby Manhire, former Guardian journalist now back in his native New Zealand, reports:
New Zealand's civil defence minister John Carter on Radio New Zealand National, asked by [presenter] Mary Wilson whether fatalities could go into the hundreds, answered "Yes" before correcting himself and saying it was too early to estimate. He went on to say, "New Zealand needs to get prepared for being a pretty sad nation for a while."
Peter Beck, the dean of Christchurch Cathedral, says he fears there are fatalities inside the cathedral, probably from tourists visiting the city landmark, when the cathedral's tower collapsed.
"We ask you to pray for the people of Christchurch as we try to deal with this," says the dean.
Christchurch Bob Parker is now estimating that there are between 100 to 200 people alive and trapped in buildings in the central business district.
Still no news about casualties outside of Christchurch – it may be that the low-rise buildings and low density means that far fewer have been affected.
Australia's Channel 7 is streaming live video from Christchurch from TV3, most of it quite devastating:
"Christchurch tonight is a city destroyed," intones the presenter.
As evening falls in Christchurch, time for another summary:
• 65 people are confirmed dead and more deaths are expected as rescuers comb through the rubble in Christchurch's centre after a 6.3 magnitude shock hit the city during lunchhour
• Tourists were said to have been in the tower of Christchurch Cathedral when it collapsed, and they are feared dead
• Power and water supplies have been cut off within most of the city, with an evacuation from the city centre being ordered
• Search and rescue teams are trying to reach the 100 to 200 people thought to be still trapped inside collapsed buidlings
• Towns outside Christchurch closer to the centre of the earthquake are also said to be devastated
I've had a few requests for information about making donations to victims of the Christchurch earthquake:
Salvation Army Canterbury earthquake appeal
Sad news from the port town of Lyttleton, near the epicentre of the quake, which sounds particularly hard hit.
Channel 7 is interviewing Valda Smith, who lives in Lyttleton, who says she put a recycling bin over her head to protect it from falling bricks during the earthquake.
The New Zealand Press Association reports that Christchurch's hospital are bracing for pregnant women going into premature labour as a result of today's earthquake – a phenomenon observed during the severe September quake last year.
One building that did survive unscathed in the centre of Christchurch was the city's excellent new art gallery – which for the second time in six months has been pressed into service as a civil defence headquarters.
Who says art is useless in a crisis?
The latest news is that the centre of the city has been cordoned off with New Zealand army troops – who happened to be in the region for an exercise – while the schools are expected to be closed for at least the next two days.
With that, let me hand this live blog back over to Lee Glendinning for more news.
Here is a powerful picture gallery put together by ABC news Australia which shows devastating scenes and damage across Christchurch.
In Australia, where I am writing, the Foreign minister Kevin Rudd has sent a 40-strong search and rescue team to Christchurch to aid the rescue effort. Rudd added that there were about 8,000 Australians in the region at the time of the quake. Australians in New Zealand can phone DFAT on +61 2 6261 3305 or the High Commission in the country on +64 473 6411 if they need information.
David Meates, the chief executive of the Canterbury Health Board, said Christchurch hospital has had an influx of injured patients.
We've had a lot of people at the emergency department...a significant number, a lot of major injuries. They are largely crushes and cuts types of injuries and chest pain as well.
Some of the more seriously injured could be evacuated to other cities, where hospitals have been put on alert and prepared to accept casualties, he said.
The Press Association has been talking to British tourists in Christchurch. Christopher Ratcliffe, 27, from Sutton Coldfield, West Midlands was forced to shelter under a desk in Christchurch library when the quake struck.
The building started to shake, my computer screen started to flicker and then the books started to fly off the shelves so I just dived under my desk.
I have experienced a few aftershocks before this, but this was totally different.
When I came outside the city looked like a bomb had hit it. There was dust and smoke in the air and bits of glass and rubble falling from the tops of buildings. People were walking around covered in blood and in tears - it was just shocking.
Our correspondent in Japan, Justin McCurry, says Japanese media are reporting that 23 Japanese students from a foreign-language school are trapped under a collapsed building in Christchurch. According to the Yomiuri Shimbun's online Japanese edition, responses have been heard from nine students trapped beneath
the rubble. The students, from Toyama city, were eating lunch when the earthquake struck. Rescue workers are at the scene, the Yomiuri says.
NNN television news network has quoted Toyama city authorities as saying that three of the students have been taken to hospital, one in a serious condition.
Here is some amazing footage of a woman being rescued from the top of a collapsed building, courtesy of TV3 New Zealand and Channel 9 Australia.
Defence Secretary Liam Fox said that the UK would offer New Zealand any help needed, telling the BBC:
I'm due to speak to my counterpart in New Zealand in half an hour or so and any help the UK can give, we will do that. Our thoughts and prayers are with the people of Christchurch today.
An update from Justin McCurry in Tokyo on the Japanese students trapped in the quake aftermath.
The Sankei Shimbun newspaper is reporting that two Japanese teachers and nine students have been rescued in Christchurch, but that 12 other students are still missing beneath the rubble.
Gary Gibson, a seismologist at Australia's Melbourne University, explains the significance of the quake being of ''shallow depth".
The critical issue with this earthquake was that the epicentre was at shallow depth under Christchurch, so many people were within 10 to 20 kilometres (6 to 12 miles) of the fault rupture. Its effect depends on how close it is, and ground shaking will be severe within 10 to 20 kilometres of the rupture.
The FCO press office has sent out a statement from the Foreign secretary William Hague.
I was shocked and saddened to hear of the devastating earthquake that struck Christchurch earlier today killing so many people. The ties that bind the UK with New Zealand are very close and my thoughts are with the friends and families of all those who have lost their lives and been affected by the earthquake.
Many people in the UK with links to New Zealand will be watching anxiously as the situation develops. Our High Commissioner in New Zealand is on her way to Christchurch and we stand ready to provide any assistance that we can to the authorities and to any British Nationals who have been caught up in the earthquake.
A final post before I hand you over to my colleague Mark Tran who is going to continue live blogging developments in New Zealand as they unfold. Here is a summary of how things stand:
• Just before 1pm local time the city of Christchurch was hit by a major earthquake registering 6.3 on the Richter scale, close to the surface, making it more damaging than the 7.1 scale shock that hit the city in September
• Police have confirmed that at least 65 people have been killed and an unknown amount of people remain trapped.
• Prime Minister John Key has called the scene one of ''utter devastation".
"This may be New Zealand's darkest day," he said.
• The quake is the second major one to hit Christchurch, a city of 350,000, in five months.
You can keep up to date with all the latest information coming out of New Zealand with Mark Tran here.