Christchurch aftershocks: A city on the edge

This clifftop home in Kinsey Tce, Sumner, was torn apart by a rockslide that smashed part of it into pieces far below. Photo / Mark Mitchell

"A lot of people have lost the plot here. They can't take it any more. You can't blame them, really."

Alan Harris lives in Kinsey Tce, a clifftop street in the Christchurch seaside suburb of Sumner, where residents were last night leaving in droves after being hammered by rockslides caused by yesterday's two big earthquakes.

A neighbour's home was torn in two, one half turned into debris amid the rubble at the foot of the cliff far below.

Mr Harris guessed up to one-third of the Kinsey Tce homes were "shattered" by falling boulders and were uninhabitable. Roads and driveways were split by deep craters.

Cantabrians had been slowly becoming used to the earth rumbling, Mr Harris said, but the 5.5 and 6.0 magnitude aftershocks yesterday were "something else".

Christchurch was again plunged into a chaos of silt geysers, dustclouds, rockslides, traffic jams and collapsing buildings.

No one was killed, but at least 46 people were taken to hospital with injuries.

Canterbury District Health Board chief executive David Meates said most of the injuries came from people being knocked over, hitting walls or being struck by falling objects.

Mr Harris said people were abandoning their homes because of the constant aftershocks and another loss of electricity.

For several hours yesterday, the area was shaken by frequent tremors.

Mr Harris clung to his kitchen bench when each of the powerful jolts hit.

"You could feel them coming, with that great thundering rumble. They came up and really just grabbed you in the throat.

"You can't walk anywhere or run anywhere because it's like trying to run against a tide - you grip the nearest solid thing."

Stuart Taylor owns Sumner Marine Services and was working on cars when the ground started to shake, dislodging boulders up to a metre wide from the hills above.

"It was worse than the one in February. The devastation is much, much worse. You have no idea."

Mr Taylor said he heard a "sonic boom" rumble through the hills when the 5.5 and the 6.0 aftershocks struck.

"We saw massive red rocks rolling down the hills and crashing through houses. They made a huge mess. It was more than you would ever wish to comprehend."

Sumner resident Paula Sinclair was told last week that the cliff overshadowing her home was safe.

Last night, she and friend Brian Lucas were looking at a rock the size of a bus which crashed on to the road metres from the house.

Ms Lucas wasn't at home when the big rock fell - she moved out of her Heberden Ave home after the February 22 quake "because I was so worried about the cliff and totally freaked out".

She came back last night after the shocks to check on her property.

"We were given word from a geotechnician just the other day that he thought the cliff was safe," she said

Next door, Tom Van Bodegraven and his wife were preparing to sleep in a tent in their back garden, too frightened to spend the night in their home.

"It's just the relentless aftershocks every 10 minutes and it's a 100-year-old house."

The already-frayed nerves of residents will be tested again by dozens of minor aftershocks from the magnitude 6.0 shake yesterday.

The big quake of February 22 was measured at 6.3.

Yesterday's magnitude 5.5 quake struck at 1pm, 11km underground and 10km east of Christchurch at Taylor's Mistake beach.

It was followed at 2.20pm by the more powerful quake, 9km underground and centred 10km southeast of the city.

Another 50 buildings in the city centre may have to be demolished, which could speed up the rebuilding of the city, said Roger Sutton on his first day as chief executive of the Canterbury Earthquake Recovery Authority.

All schools and early childhood education services will be closed today, so the Education Ministry can check them for damage.

Christchurch Mayor Bob Parker decided against declaring a state of emergency, but described the 6.0 quake as "very, very scary".

"Thank God, we had evacuated the whole of red zone - there's been quite clearly a more significant building collapse in there," he said.

"We are now being enveloped by dust blowing out of the central city, we are just outside the cordon.

"This time a plethora of sirens have gone off ... car sirens, building sirens, it's just terrible."

Prime Minister John Key said the tremors were another blow to Christchurch residents, who had already endured so much.

"However, today's events in no way weaken the Government's long term commitment to rebuild Christchurch and surrounding areas," he said.

Power was cut to about 56,000 households and businesses - just over 25 per cent of provider Orion's customers.

By 8.30pm, 20,000 homes and businesses were still without power.

Telecom and Vodafone mobile networks were affected by congestion, and the companies urged customers to confine phone use to emergency calling and use texting to conserve capacity on the mobile networks.