A series of strong quakes, including a 6.0-magnitude tremor, rocked New Zealand's Christchurch on Monday, causing one building to collapse and fraying nerves in the stricken city.

Prime Minister John Key said power had been cut to some 6,000 homes after the quakes, in which 10 people were injured by falling debris but no-one killed, according to initial figures gathered from emergency personnel.

The US Geological Survey and New Zealand authorities measured Monday's biggest quake at magnitude 6.0, placing the epicentre nine kilometres (5.6 miles) deep and within 14 kilometres of the country's second largest city.

The major aftershock followed a string of earlier tremors, including a 5.2-magnitude jolt which caused building damage in the city, which is still recovering from a magnitude 6.3 quake in February which killed 181 people.

"These latest aftershocks have caused a renewed level of concern and upset for Christchurch residents who have found them frightening and unsettling," the prime minister said.

"However, today's event in no way weakens the government's long-term commitment to rebuild Christchurch and its surrounding areas."

Christchurch mayor Bob Parker agreed it had been "a nasty shake".

"People will be shaken. I don't think we are going to come out of this completely unscathed," he told Sky News.

Police confirmed that a structure had fallen over in central Christchurch, much of which is still blocked off after the major earthquake earlier this year, but said nobody was trapped in the rubble.

Fire officers rescued two people from St John's Church in Latimer Square in the city centre, which was damaged by the quake.

The 6.0-magnitude shock prompted police to fully evacuate an area of the damaged central city known as the red zone, while rock falls closed several bridges and prompted the closure of one police station.

Police urged residents to check on friends and neighbours, and to stay at home and avoid travelling if possible, but residents gridlocked the roads as they attempted to find their way home and reach family.

Empty cars stood abandoned on the roads towards Christchurch, while traffic lights were out in much of the city.

Local Richard Wills said he was inside his apartment when the first quake hit, knocking items off shelves.

"The second one was appreciably more violent," he told AFP.

Wills said the series of quakes, following earlier tremors, was preying on people's nerves, many of whom had their homes or businesses destroyed by the February upheaval and were still experiencing regular aftershocks.

"I feel very, very sorry for them, I wouldn't like to be in their position," Wills said.

The series of quakes came just hours after the opening of an inquest examining why an office block collapsed in February's earthquake, killing more than 100 people, including 65 foreign students.

When the first tremors hit around lunchtime, lawyers and relatives of those killed when the Canterbury Television (CTV) building toppled and then burst into flames on February 22 fled the building as windows rattled.

Geoscience Australia seismologist David Jepson said people would have been shaken quite strongly after New Zealand's South Island had endured much seismic activity in recent months.

"It seems like they are going to keep happening. Since they had that really big earthquake it seems to me like it activated all these different faults. But it's just a guessing game what is going to happen next," he said.

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