Christchurch left devastated on New Zealand's 'darkest day'

More than 300 people were still trapped in collapsed buildings last night after a massive earthquake hit New Zealand's second biggest city, Christchurch, claiming at least 75 lives and destroying buildings.

As police, emergency services and hospitals struggled to cope with the disaster, which toppled the spire of Christchurch's stone cathedral, the New Zealand Prime Minister, John Key, declared a national state of emergency.

This morning, Mr Key vowed that Christchurch's "comeback" would begin today. "Though lost lives will never be replaced, and though your city will never look the same again, you will rebuild your city, you will rebuild your lives, you will overcome," he said.

He had earlier referred to the disaster as "New Zealand's darkest day" and described the city as "just a scene of utter devastation".

Police Superintendent Russell Gibson said the death toll was likely to rise. "There are bodies littering the streets, they're trapped in cars, crushed under rubble and where they are clearly deceased, our focus unfortunately at this time has turned to the living," he said.

Rescuers pulled 30 survivors from collapsed buildings during the night, pushing the total number brought out alive to 125. Some emerged with barely a scratch, according to Supt Gibson. Others were required to have limbs amputated in order to be freed.

Christchurch was struck by a 7.1-magnitude earthquake last September, which caused widespread damage but no deaths mainly because it struck before dawn on a weekend. Yesterday's 6.3 tremor – technically an aftershock from September – was far more destructive because it was shallower and closer to the city. And it came at the worst possible time: a weekday lunch-hour.

The streets of this most English of New Zealand cities, population 350,000, that is bisected by the willow-lined River Avon, were packed with office workers, shoppers and tourists. The quake transported them into a rubble-strewn landscape through which dazed and bleeding survivors wandered amid the screams of the injured and trapped.

The city's airport was closed to all but emergency flights yesterday, and the main hospital was temporarily evacuated. Roads and pavements buckled and split, power and telephone lines were knocked out and pipes burst, flooding the streets.

Firefighters using helicopters and giant cranes rescued survivors from roofs and the upper storeys of high-rises. But with the emergency services overwhelmed during a day of chaos, civilians dug through the rubble with bare hands to help free people who were trapped. They ferried the injured to private cars on stretchers made from rugs or pieces of debris.

Barnaby Luck, a tourist from Pembrokeshire, dived under his hostel bunk bed when the shock hit at 12.51pm. "Everything started shaking, and it became more and more violent," he said. "It was like someone had got hold of the building and was shaking it and swinging it back and forwards."

Trapped in her destroyed office building, Ann Voss rang her children to say goodbye. Six hours later she was freed. She told New Zealand television she had crawled under her desk but that the ceiling collapsed on top of it. She communicated with other survivors in the building by calling out to them and knocking on the rubble, she said.

As darkness fell, emergency teams continued to work under lights and in rain. Their efforts were focused on two buildings: a financial services block whose four storeys had concertinaed and the offices of the local Canterbury Television (CTV), which also housed an English-language school.

Twelve Japanese students were missing in the wake of the disaster, which was followed by two large aftershocks and multiple smaller tremors. Police said other reported deaths included the occupants of two buses crushed by falling buildings. Bodies were also pulled from a hostel and a bookshop, and a tourist was killed in a van, according to local television.

One survivor, Nathanael Boehm, said he saw people buried under tons of concrete when buildings collapsed. Mr Key said: "What was a vibrant city a few hours ago has been brought to its knees."

New Zealand is one of the world's most earthquake-prone countries with more than 14,000 a year, although fewer than 10 cause damage. All schoolchildren are taught that when a quake strikes they must get under their desks or stand in a doorway. The capital, Wellington, is built on five significant fault lines.

In Christchurch, in the South Island, with its historic stone buildings and streets named after English cathedral cities, rebuilding was still continuing after the September tremor. Many buildings were unstable as a result of that quake, which caused an estimated NZ$4bn (£1.85bn) of damage.

According to the US Geological Survey, the epicentre of yesterday's quake was just three miles from the city centre and only 2.5 miles underground. It was felt across large parts of the island and caused damage in nearby towns.

Pip Ramby was on the fifth floor of the CTV building when it happened. Afterwards, she realised she ended up almost at ground level. People outside pulled her and some colleagues to safety, but two of them were badly injured, she said.

Bob Parker, the city's Mayor, called the quake an "unbelievable tragedy".

Timeline: Christchurch earthquake

12:51 on Tuesday (23:51 on Monday GMT) New Zealand's second-largest city is struck by an earthquake measuring 6.3 in magnitude on a busy working day. Hundreds are thought to be trapped.

13.00 Government opposition leader Phil Goff tweets: "We're ok – been evacuated from the airport and we're in the carpark now. Lots of upset & scared people around."

14:47 Australia pledges to send rescue teams to help search for survivors. Aftershocks fuel fears of further building collapses. Reporters describe hearing screams from trapped city residents.

15.01 Deputy Prime Minister Bill English says the government is "gearing up for something larger, more devastating" than last year's quake in Christchurch.

15.12 TV station says there are no ambulances left to take injured to hospital.

16:30 Prime Minister John Key says at least 65 people are thought to be dead.

20:00 Scientists report that the quake caused around 30 million tons of ice to break off New Zealand's biggest glacier.

22:43 Reports say rescuers have pulled 125 survivors from the rubble.