New Zealand on Tuesday said the latest Christchurch earthquake had killed one man and also confirmed fears that thousands of homes in the city would have to be abandoned.

As Christchurch began the all-too familiar routine of cleaning up after its third major quake in nine months, Prime Minister John Key said the repeated seismic pounding had made the land in some areas too unstable to rebuild on.

"There are certainly in the order of thousands of homes that are affected," Key told reporters in Christchurch after assessing the damage from Monday's 6.0-magnitude tremor.

As aftershocks of up to 4.2 continued to rock the city Tuesday, Key said the quake exacerbated land damage caused after a devastating 6.3 jolt in February that killed 181 people and another 7.0 tremor in September.

"We now have a reasonably clear picture about what land won't be able to be rebuilt on," he said, adding residents would be informed whether they had to abandon their properties after payout options had been finalised with insurers.

Monday's quake opened up sink holes in roads, burst water mains and toppled already weakened buildings in the city centre.

In what mayor Bob Parker described as "a very rough night in the city", 20,000 homes were without power in the bitter cold and nerves were frayed when a 4.7 aftershock jolted residents awake at 2:48am (1428 GMT Monday).

Parker initially said the city could take comfort in the fact that there were no fatalities, but even that consolation was stripped away when the Canterbury health board confirmed the tremors killed a nursing home resident.

The board said the elderly man died as a direct result of Monday's quakes but further details were not available.

The number of people injured was also revised up from 10 to 45, two of whom remained in Christchurch Hospital.

Businessman Joe Arts said the latest tremors were a major setback for New Zealand's second largest city.

"It's like we've gone backwards," he told AFP as he surveyed his city centre printing shop, which was damaged but remained open after September's quake but has been closed since the February disaster.

"It's over now, I'll just wait for the insurance payout."

At the beachside suburb of Sumner, the wreckage of a house that tumbled down a cliff was cordoned off as work began to stabilise other homes teetering precariously on the edge.

Schools remained closed, elective surgery was cancelled in hospitals and a welfare centre was set up in the suburb of Aranui for people unable to return to their homes.

But emergency crews, now well-drilled in earthquake repairs, began work at first light and had restored water and electricity to most of the city by late Tuesday.

Key did not expect the latest shake to have a major impact on the NZ$15 billion ($12.3 billion) Christchurch rebuilding programme, saying the worst-hit areas had already suffered major damage in the previous quakes.

"It hasn't had a big impact on the rebuild here in Christchurch because it was a mirror footprint really," he said.

"It's for the most part damaged buildings that were already damaged."

The worst-hit area was the already devastated downtown area known as the red zone, which remains off-limits to the public following the earlier earthquakes.

Key said 75 buildings in the area previously believed safe had been comdemned following Monday's quake, bringing the total earmarked for demolition in the central business district after the three quakes to about 900.

A predicted exodus from Christchurch after the February quake failed to happen but Leanne Curtis from community group CanCERN said Monday's scare would be the final straw for some.

"People just can't do it any more," she told Fairfax Media. "We're back to square one."

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