LATEST: A major search and rescue operation is underway in Christchurch this morning where at least 100 people remain trapped under rubble.
Construction workers and search and rescue specialists toiled under floodlights to dig out survivors and the dead from buildings flattened by the earthquake that ripped the city apart.
Dozens of search and rescue and medical staff have arrived to continue with the frantic recovery effort.
Yesterday's earthquake has claimed at least 65 lives and scores more are injured in what Prime Minister John Key says "may well be New Zealand's darkest day".
The death toll is already the second highest from a New Zealand earthquake - outranked only by the 256 people killed in the violent 7.9 1931 Hawke's Bay quake, whose 70th anniversary was marked earlier this month.
Police have reported "multiple fatalities" at several locations in the downtown area, including in buses crushed by falling buildings.
Buildings have been destroyed with at least 100 people believed to be trapped inside. Rescuers warned some people remained trapped overnight.
More bodies were likely to be pulled from the rubble of the Canterbury Television building which collapsed in the earthquake, a man involved in assisting rescue teams in their hunt for survivors said tonight.
The Southern Demolition employee, who did not want to be named, told NZPA rescue personnel pulled bodies from the rubble while he was assisting in the recovery effort.
"We were working on one side of the building and on that side we managed to pull one person alive but we also pulled out a body. On the other side they pulled out four or five - I don't know if they were dead or alive.
"It was awful," he said.
He said rescue personnel were risking their lives to jack up parts of the building allow members of urban search and rescue to look for survivors.
"Those guys are brilliant. They get in there where they shouldn't be and if they hear anything everything is turned off while they locate where the sound is coming from," he said.
At a press conference after 8.30pm last night, Deputy Prime Minister Bill English said Cabinet had made available emergency funds for the recovery operation.
The Government was willing to throw every effort at the recovery, English said. "Time is now of the essence."
English said the scale of destruction and loss of life in Christchurch "is becoming obvious".
A large number of people were simply too traumatised to get themselves home tonight, he said.
TOLL COULD RISE
Christchurch Mayor Bob Parker has told TVNZ the death toll could double.
It could be later this morning before the number of missing is known.
The next official update is expected at 5.30am today when Civil Defence will hold a press conference in the Beehive bunker.
Up to 31 Japanese students from a foreign-language school are believed to among those trapped under collapsed buildings in the city.
The students, from Toyama city, were eating lunch when the earthquake struck. There are reports three of the students have been taken to hospital, one in a serious condition.
According to the Yomiuri Shimbun's online Japanese edition, responses have been heard from nine of the trapped students.
The Pyne Gould Guinness building has tilted at an awkward angle and slumped to the ground with 30 people thought to be inside, while people are trapped under desks in the Christchurch Press building opposite Christ Church Cathedral.
Fatalities have been reported in the Canterbury TV building, while the Forsyth Barr Tower has lost its stairs, so those trapped high above ground had to be lifted out by crane.
People are also feared trapped in hotels, Civil Defence Minister John Carter said.
"What we don't know is whether they were out looking around the town or were in their rooms."
Christchurch Hospital is operational but people are being asked to keep the Emergency Department for major casualties only.
A generator has been brought in to maintain power supply at Christchurch Hospital Riverside Block. "If power is not fully restored this evening patients at Christchurch Hospital's Riverside Block may need to be evacuated," a statement said.
SUPPORT ARRIVES FOR LONG NIGHT
A Royal New Air Force Boeing 757 was due to land in Christchurch from Whenuapai Air Force Base at 10.30pm last night carrying 54 search and rescue staff, plus 20 St John's medical staff.
More than 200 soldiers are assisting NZ Police with cordon duties and the Navy's vessel Canterbury docked in Lyttelton has offloaded around 160 persons for cordon support duties.
Two Iroquois helicopters from Ohakea have arrived to assist with rescue efforts in the city. Other Navy ships are also on the way.
The NZ Army's medical teams are at four different locations around Christchurch with military officers working with the Police. NZ Defence Force firefighters are working with local fire brigades.
English said the force of the earthquake was above the limit modern buildings were designed to withstand.
An estimated 1200 people sheltered in Addington overnight, while nurses with specialist intensive care skills are being flown to the city.
Schools are closed until further notice.
Residents have been told to stay at home and save any safe water for drinking, including rain water which could be collected as rain falls tonight as the city's reservoirs have been shut down. Toilets should not be flushed and water should be boiled as sewage systems have failed, Parker said.
Parker said up to 25 buildings of significant size in the city were probably damaged beyond repair.
Hospitals around the South Island were being cleared to take the hundreds of casualties expected, while makeshift hospitals were being set up in parts of Christchurch.
Emergency triage centres for the injured are operating at Latimer Square, Canterbury University and the Sanitarium Building in Papanui - not South City or the Spotlight Mall, Sydenham, police said.
"This is a big problem. Far worse in casualties than the 4th of September, largely because it happened at a different time of the day," Civil Defence director John Hamilton said.
SCREAMS FROM COLLAPSED BUILDING
Pyne Gould Corporation has confirmed that staff from the building are missing, but would not say how many. The company was working to account for each staff member.
People died when buses were crushed under falling building facades, Radio NZ reported.
At the building's cordon, Labour Party leader Phil Goff said earlier this evening that at least 30 people were feared trapped inside and at least one person was killed. Families were congregating at the cordon, he said.
Parker said: "There are people fighting for their lives at the moment but there are also people fighting for them."
"We're in the middle of an extremely serious situation. We're preparing ourselves for what I think will be a really sad, bleak day for our city but be reassured everybody is doing what they can."
Parker said there were currently people still trapped in cars and buildings, with some being able to phone to say they're trapped.
Defence Forces have been called in to assist with the earthquake recovery and were going door to door checking on residents.
The airport was closed to all but emergency flights and Lyttelton tunnel was shut.
Christchurch Hospital remained open but was also damaged. It asked that only seriously injured people come to the emergency department. It had a full emergency plan in operation.
Power should return to half of Christchurch tonight, with most of the city back on in the next three to four days, lines company Orion said.
St John's Ambulance had run out of ambulances and was using four wheel drives to get the injured out.
The New Zealand Blood Service has been flooded with calls from people wanting to donate blood.
The service said it presently had adequate blood stock, but would advise through its Facebook page and website if that changed.
COLD, WET NIGHT FOR RESIDENTS
Thousands of homeless Christchurch residents are tonight bracing for a long, cold, wet and worrying night in welfare centres.
The Christchurch City Council said a welfare centre at Addington Raceway had closed due to high umbers, believed to be about 1200.
People were instead asked to go to Burnside School, Papanui High School, the Lyttelton Recreation Centre, Brooklands Community Centre or Akaroa Senior School.
WeatherWatch.co.nz said the temperature was expected to fall to 9-10degC overnight, compounded by light rain. Many more aftershocks were also expected.
However, the showers should clear in the morning and a high of 18degC was expected.
An Urban Search and Rescue team (SAR) from Australia would arrive after midnight.
Two New Zealand SAR teams were on their way as well as ambulances from around the South Island.
Some critical patients had been flown from Christchurch to other hospitals around the South Island.
Military personnel were being coordinated to make areas safe.
CATHEDRAL, HOTELS DAMAGED
The spire of Christchurch Cathedral, the heart of the city, has collapsed.
Dean of Cathedral Peter Beck said they tried to get out who they could but it was now in the hands of emergency services. "It doesn't look good".
He had "no idea" of how many people were inside.
Power was out in a significant portion of the city. While some parts will have power restored overnight it could be fours days till power was restored across the city.
A significant number of hotels have collapsed and it was not known how many people were inside, the Civil Defence Minister said earlier this afternoon.
Bodies were seen being taken out of the damaged YHA hostel in the city.
On the corner of Lichfield and High Streets, a block of shops had completely collapsed and rescue services believed four or five people are trapped in the rubble.
One body had been pulled from the wreckage.
People trapped in the CBD have put signs up at the windows saying 'HELP'.
Helicopters were being used to put out fires in the central city.
Amber Armitage said people were wandering around central Christchurch trying to get out but all exits from the city were blocked.
There was a strong smell of gas and clouds of dust.
A bus on Colombo St was "completely trapped under bricks" and people were working to free passengers trapped in it.
She said the quake felt much stronger than the 7.1 quake on September 4, 2010 and believed the city was "irreparable".
Former Blenheim woman Joh Bloomberg was working in Ballantynes department store in central Christchurch when the earthquake struck.
"I was clinging to this cupboard next to my desk. I thought it was going to be fine, but it got worse and worse, and went on for so long. It's the worst one I've felt."
She walked outside to nearby Lichfield St and saw a car flattened by a fallen section of building.
"I'm normally pretty calm with things like this but when I saw a huge concrete slab on top of that car ...
"It's squashed down to zero. You never think you'll see anything like that."
Everyone was screaming as they left the store.
A colleague of Miss Bloomberg's walked outside to Cashel St mall and saw people lying on the ground who she thought had been hit by falling rubble from a nearby cafe.
Kay Cowlishaw said there was destruction everywhere.
"There's just water pouring out and sewerage, the whole garage is filled with water. There are cracks in the road.
Sally Blundell lives in Opawa and said their whole house shifted on its piles.
"We have no water, no power. We are really shaken. Most of us do not know what has happened to the inner city. We are just hearing reports on the radio and it sounds really frightening. The ground is still like jelly, a low level shake all the time."
Malcolm, a policeman from Darfield, was driving in the city when the earthquake hit.
"I thought I had a flat tyre, then the place was shaking like hell."
He said oak trees in the Hagley Park had been uprooted and fallen across tents.
"I'm shaken, I'm at Christ College now and the school is a shambles - there's a lot of damage to the buildings.
"All of the water pipes are burst and it looks like a tsunami coming across the park."
"It's just unbelievable - just the sheer power."
His daughter was at Rangi Ruru school and she said students were running around screaming.
HOSPITAL INUNDATED WITH WOUNDED
A patient in Christchurch Hospital, who was in the riverside block when the first quake hit, said things were falling down and some elderly people were injured in the stairs.
"It was just a lot of panic. The nurses and doctors were quite calm but I think just like the first time, it was all quiet, then all of a sudden there was panic."
Christchurch Hospital is operational but people are being asked to keep the Emergency Department for major casualties only.
The hospital, along with most other hospitals in the region has suffered infrastructure damage, a Health Ministry statement said.
A generator has been brought in to maintain power supply at Christchurch Hospital Riverside Block. "If power is not fully restored this evening patients at Christchurch Hospital's Riverside Block may need to be evacuated."
Large volumes of patients are being triaged through the Christchurch Hospital ED, many with serious injuries. Patients with non-life threatening injuries are being assessed and treated in Christchurch Women's Hospital and the Outpatients Department.
Patients from the top two floors of Christchurch Hospital have been evacuated to lower floors. There is some water damage throughout the hospital but staff are awaiting further assessments.
St John district commander Tony Dowell said they had been seeing a range of injuries from serious to minor.
Mostly of the injuries were from crushing. St John was mobilising resources from West Coast, Dunedin, Nelson and South Canterbury.
The National Crisis Centre in Auckland had also been activated.
FELT MORE STRONGLY THAN SEPTEMBER QUAKE
Today's 6.3 earthquake would have felt more powerful for Christchurch residents than the original quake on September 4.
GNS duty seismologist Bill Fry said the acceleration of today's earthquake was larger in Christchurch city than the magnitude 7 earthquake last year.
"Instantaneously, they would have felt the greatest amount of shaking today. But the duration would not have been as long."
The earthquake happened at a shallow depth of five to six kilometres below ground.
In the city, the acceleration measured the same as the force of gravity.
In September, the largest acceleration felt around the city was on its eastern side, and this measured 0.8 times the force of gravity.
Today's earthquake did not last as long as the September quake, but Dr Fry said its duration had not been confirmed yet.