Devastated Christchurch will be uninhabitable for months

With a possible toll of up to 350 dead, last week's earthquake may be New Zealand's worst disaster

The earthquake in Christchurch may go down as New Zealand's worst disaster, according to the Prime Minister, John Key, as the death toll reached 145 with more than 200 people missing. And the prognosis for the city centre will do nothing to lift spirits. Engineers and planners said the devastated centre may be completely unusable for months and that at least a third of the buildings must be razed and rebuilt after last Tuesday's 6.3-magnitude quake.

On the outer edge of the central district, Brent Smith watched in tears as workers demolished the 1850s-era building where he lived and ran a bed and breakfast. His three daughters hugged him, also weeping. "You don't know whether to laugh or cry, but I've been doing more of the latter," Mr Smith said.

Mr Key said his government would announce an aid package tomorrow for the estimated 50,000 people who will be out of work for months due to the city centre's closure. Mr Key, who spent some of the afternoon talking to families who lost loved ones in the disaster, called for two minutes of silence next Tuesday.

As bodies continue to be pulled from the wreckage, it is feared the death toll will exceed the country's previous worst disaster – the 1931 Napier earthquake on North Island in which at least 256 people died.

Christchurch's mayor, Bob Parker, assured relatives of the missing – including people from several countries who travelled to the city to await news – that every effort was being made to locate survivors.

Rescue and recovery efforts were hampered by continuing aftershocks, which sent masonry tumbling down. The multinational team of more than 600 rescuers scrabbling through wrecked buildings in the central city last pulled a survivor from the ruins at mid-afternoon on Wednesday. Four days have now passed without anyone being found alive.

The rescue co-ordinator, Jim Stuart-Black, said that rescuers continued "to look in every possible place for survivors. We are still in active rescue mode ... but we are also realistic that we are starting to move into the miracle stage of the operation," he said, with survival becoming less likely six days after the quake.

Police have said up to 120 bodies may be entombed in the ruins of the central Canterbury Television (CTV) building alone, where dozens of foreign students from an international school were believed trapped. But Christchurch Police Superintendent Russell Gibson said rescuers weren't completely ruling out good news. "I have talked to experts who say they've worked on buildings like this overseas and get miracles. New Zealand deserves a few miracles," he said.

The King's Education language school released a list of missing people presumed to be in the building: nine teachers and 51 students – 26 Japanese, 14 Chinese, six Filipinos, three Thais, one South Korean and one Czech. An additional 19 students were listed as "status unknown".

The central area of Christchurch, one of New Zealand's three main cities and a picturesque tourist hub of 350,000 people, radiates outwards from the cathedral plaza. The Avon River meanders through a mostly low-rise city dotted with greenery and old stone buildings – many brought down by the quake – that imparted an Old England character.

The cathedral survived another quake last September with only minor damage. But when the ground moved again on Tuesday, it suffered as cruelly as the city in which it stood.

The body of the cathedral remained in one piece, but its spire toppled into Cathedral Square. This was followed by a cascade of masonry, which lies in deep drifts around the main entrance. The roof was pierced by falling stones, leaving the altar and pews open to the sky.

It was a sad day for Christchurch, said Tina Macdonald, 55, who works at a motel and considers the building one of the city's main draws. "It's an icon," she said. "It was such a beautiful building; people would go there just to sit in the quietness."

Before any rebuilding can begin, crews must clear the rubble and search for the 22 people believed to be buried inside. Many of those missing were part of a tour group which had just begun to climb the bell tower to take advantage of its panoramic views of the city. They may be trapped under rubble near the tower's base. That work began on Friday, but aftershocks brought new slabs of masonry down, and the work was delayed again on Saturday.

The city's central business district will take months to recover, said Gerry Brownlee, the earthquake recovery minister, adding that "most of the services, in fact all, offered in the area will need to relocate elsewhere".

Damaged buildings will need to be bulldozed and rebuilt "so that people can have confidence about coming back into the area to transact any business that's here", Mr Brownlee said. One in three of the city centre's buildings were so severely damaged that they must be demolished, Jason Ingham, an earthquake engineer, said.

One family spent yesterday retrieving a handful of salvagable belongings from their home – a couple of blankets, a stack of dishes, a Mickey Mouse mug and a box of crackers. They're staying with friends, but hope to buy a camper van. Maree Butcher, 49, said she awakes with memories of Tuesday's horror every morning at around 3.30. She lies in bed and stares at her husband, Norm, who was nearly killed racing out of the back door as the brick walls blew out around him and the upstairs collapsed to the ground. Nodding at the wreckage, Mr Butcher said: "I really did want the open entertainment area." His wife smiled. "We've lost our house and belongings," she said. "But we're still alive."