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.
"When it hit we were knocked to our feet. Everything in the house fell down, nothing was left still standing. There's more damage than the first earthquake, the roads are completely torn up; sewage coming up and flooding. It's crazy."
"The elderly are all crying. The next-door neighbours around us were all bawling their eyes out, it was horrible. People can't get out of their houses," said Mr Katene.
"We've seen cars halfway sunken into the road. We've heard there's a bus which is sunken halfway into the road just around the corner.
"Buildings are half-collapsed everywhere.
"It smells horrible. The roads are packed with cars. There aren't enough police or ambulances. Houses are all collapsing. It's pretty shocking; a total warzone."
Aftershocks continue
GNS Science said today's 12.51pm quake was centred at Lyttelton at a depth of 5km.
It was followed by a 5.7 magnitude aftershock at 1.04pm at a depth of 6km, 10km south of Christchurch.
A magnitude 5.5 aftershock was recorded within five kilometres of Lyttelton - the town at the epicentre of a huge earthquake that hit Canterbury today.
The large aftershock was recorded at 2:50pm at a depth of 5km.
A magnitude 4.6 shock hit at 3.38pm, centred 10km east of Lyttelton. That was followed by another five minutes later, a 4.5 shake 10km south-west of Christchurch.
The third took place at 4.04pm and measured 4.6, within 5km of Christchurch, taking the total to 10 aftershocks since the 6.3 earthquake at 12.51pm.
Buses crushed, buildings collapse
Christchurch resident Jane Smith, who works in the central city, earlier told the Herald a work colleague had helped with rescue efforts after a building facade collapsed on a bus on Colombo St.
"There's people dead. He was pulling them out of a bus. Colombo St is completely munted," she said.
TV3 reports there are 24 people trapped on the 17th floor of the Forsyth Barr building who are being rescued
TV3 also reports that a person had died in the Christchurch suburb of Sumner and a body has been carried out of Christchurch's YHA hostel.
The broadcaster showed footage of people being rescued from the Pyne Guinness Gould building, where it is believed some 200 people have been trapped.
It said the Provincial Chambers Building had also collapsed and more people were likely also trapped there.
A listener told Newstalk ZB that the Piko Wholefoods building on Kilmore Street near the city centre, which was hit in the September 4 earthquake, was now "practically non-existent".
Herald reporter Jarrod Booker said Christchurch's historic cathedral of the Blessed Sacrament on Barbadoes Street had half collapsed, with the remaining part of the building filled with cracks.
The spire on the Christchurch Cathedral has also collapsed.
Christchurch resident Gary Moore told NZPA he and 19 other colleagues were trapped in Christchurch's Forsyth Barr building on Colombo Street.
Mr Moore said workers were stuck on the 12th floor as the stairwell had collapsed. He was not sure if people were trapped on other floors.
'Grave concerns' for Banks Peninsula
Christchurch Mayor Bob Parker says he holds grave concerns for the safety of people in Banks Peninsula area following today's massive earthquake and aftershocks.
Christchurch is located immediately north of the peninsula.
"We still have yet to hear any reports in from Banks Peninsula and I'm very very concerned about that," he told Radio New Zealand.
"The centre of the earthquake was in Lyttelton Harbour. There are hills covered in rocks, those rocks would have come down."
Mr Parker said the damage to the city centre was immense and people were trapped in buildings.
"Everybody needs to understand that this is going to be a day of very black news," he said.
Canterbury would need help from the rest of the country.
"There is no doubt that we are going to have a significant number of homeless people in our city," he said.
The region had lost a lot of communication, and water was coming up through the streets from pipes.
He urged people to stay calm despite the extremely difficult circumstances.
Mr Parker said people were very frightened but they needed to keep the roads clear.
"Don't use the phones unless you have to, those phones are also our lifeline."
When the quake struck the mayor was knocked over.
"I looked out over the city once I got up and I could see clouds of dust from buildings collapsing. I could hear screams from streets."
Traffic gridlock
Jarrod Booker said queues of cars could be seen being shaken up and down when the latest aftershock hit.
Mr Booker said cars stuck in the city's gridlock were being rocked side to side and occupants could be heard screaming.
"Even sitting in a car you can feel continual shaking on a smaller scale than the original quake," he earlier said.
Emergency services have been struggling to access the central city and were having to manoeuvre slowly around gridlocked traffic.
Mr Booker said Tuam Street had become a river as water poured from ruptures in the road and was impassable in places.
The whole central city was in gridlock as people tried to evacuate central businesses to check their homes, he said.
Most traffic lights were out and cars were also having to negotiate around hordes of people on foot.
Some pedestrians were standing on the footpaths and staring into space, apparently in shock.
Mr Booker said the southern suburbs appeared to be particularly badly hit.
Liquefaction was forcing tarmac up in the middle of the road and water and sand were spewing out of chasms.
Civil Defence response
Police said all available staff were helping with the rescue operation and the Defence Force had been called in to assist.
Triage centres have been established for the injured at Latimer Square in the central city, Spotlight Mall in Sydenham and Sanitarium in Papanui.
Civil Defence Minister John Carter said all the South Island hospitals apart from Invercargill had been emptied to make way for earthquake victims.
Mr Carter and preparations had been made for a state of emergency to be declared.
He said the number of fatalities and the extent of the damage was still unclear.
Speaking to media at the Beehive's National Crisis Centre, Director of Civil Defence John Hamilton earlier said a response plan was now being put together using all available national resources.
"That includes extra fire people, extra police personnel, assets from the Defence Forces. International offers of assistance are coming through from Australia in particular."
Mr Hamilton said the earthquake was a level three crisis - the highest for a localised event.
Phone lines are down and calls are not being connected to emergency services. Telecom said it is working to understand which services have been affected by the earthquake and get these restored as soon as possible.
Temporary accommodation is being organised for those who have been displaced, with tents possibly to be erected in Hagley Park.
All but emergency flights into Christchurch Airport have been put on hold while it checks the state of its runway.
