Dangerous aftershocks have left the battered city of Christchurch struggling to rebuild 12 months after a devastating earthquake and raised doubts over its economic future.

Much of the downtown area was destroyed and remains sealed off following the 6.3-magnitude quake on February 22 last year, which killed 185 people as it flattened office blocks, buckled roads and brought historic buildings crashing down.

Hotels and shops lie empty behind the wire-mesh fences of the "red zone", which covers most of the central business area -- a ghost town of broken buildings and vacant lots with weeds poking out from exposed foundations.

The only sound of activity from within is the crash of rubble being dumped into skips as workers still toil to clear debris from the historic precinct which was once the pride of New Zealand's second largest city.

Plans are afoot for a NZ$30 billion ($24.5 billion) rebuilding programme, the largest construction effort in the country's history, to restore Christchurch to its former glory as capital of the South Island.

But constant seismic activity has frustrated the effort, with about 10,000 aftershocks recorded since September 2010, when a 7.0-magnitude quake on a previously unknown fault line began what has become a trial of endurance for the city.

No-one was killed in that quake and reconstruction was well under way before the deadly February tremor hit, lower in magnitude but shallower and with an epicentre much closer to the city centre's already weakened buildings.

Since then, there have been major aftershocks in June and December, the most recent sending terrified Christmas shoppers fleeing from stores in panic and adding more damage to the scarred city, further delaying reconstruction.

More than 60 percent of the old buildings that defined Christchurch, creating what locals called "a little slice of England", have been lost and many more are severely damaged and need expensive reinforcement.

Win Clark of the New Zealand Society for Earthquake Engineering said most, with the possible exception of landmark buildings such as the Anglican cathedral, would not be rebuilt because of the danger they posed.

Some have suggested simply shifting the entire CBD elsewhere to more stable ground but Clark said that was impractical.

"The problem there is that there's a very large investment in infrastructure -- buildings, water supply, power, sewerage, all types," he said.

"It's been damaged but to build a new city you would have to start over again from scratch at colossal cost."

Mayor Bob Parker last year released the local council's vision for the future, a low-rise central business district serviced by light rail with environmentally friendly buildings and large areas of parkland.

The council wants a seven-storey high limit, saying traumatised workers do not want to return to high-rise office blocks, which were the cause of most deaths when they catastrophically failed in the February shake.

Clark was sympathetic but said modern building methods using techniques such as deep foundations meant there was no engineering reason preventing the immediate construction of large buildings.

"The fact that we're going to get further aftershocks should not stop current redevelopment," he said.

New Zealand Institute of Economic Research principal economist Shamubeel Eaqub warned excessive restrictions could prompt investors to take their capital elsewhere, to cities such as Auckland, and residents would follow.

He was also concerned that ongoing delays partially blamed on infighting among officials -- Earthquake Recovery Minister Gerry Brownlee recently labelled Parker a "clown" -- was paralysing the city's regeneration.

Eaqub said 30,000 jobs had been lost in Christchurch over the past year and the longer the rebuild took, the more difficult it would be for the city to regain its mantle as an economic powerhouse.

A worst case scenario, he said, could see Christchurch -- which before the quake was the hub of a region responsible for 15 percent of New Zealand's economy -- reduced to a "rural service town".

"We're at a fork in the road and it's not really clear which of things (rebuilding plans) are working and which are not," he said, adding that the issue had implications for the wider economy.

"We just haven't had enough time to gauge some of these plans but it feels like the urgency of the situation is certainly heightening."

Amid the gloom, however, an innovative retail project just outside the red zone offers a glimpse of the dynamism Christchurch is hoping to harness in the rebuild, which is now not expected to be fully under way until next year.

Re:START is a temporary shopping centre built entirely from shipping containers, with banks, fashion boutiques, coffee shops and a post office housed in brightly coloured -- and earthquake-safe -- boxes.

"People think it's really cool," said coffee shop worker Jan-eve Burns. "It's the first time for a while that something has put a bit of life back into the city centre and Christchurch really needed it."