© Screen shot, Google Maps
The quake at a depth of 34 kilometres (21.1 miles) struck six kilometres (four miles) from Christchurch at 04:05 am (1635 GMT Friday), the USGS said.
A 7.0 magnitude earthquake rocked New Zealand's second largest city Christchurch early Saturday, causing widespread damage including the collapse of some buildings and power outages, witnesses and the U.S. geological survey said. The Civil Defence ministry said the national crisis management centre had been activated. "We've had a wide range of reports of some serious damage," a civil defence spokesman said.

Although many people with minor injuries sought treatment, hospitals said there were no reports of any serious injuries although doctors were on standby because of the intensity of the quake and the damage to buildings.

The quake struck at a depth of 16.1 kilometres some 30 kilometres northwest of Christchurch at 4:35 a.m. (11:35 a.m. ET Friday), the USGS said.

Roads in the seaside suburbs were packed with cars as residents moved inland but there were no tsunami alerts issued. A swarm of aftershocks were ongoing and police said damage was widespread throughout Christchurch, with electricity supplies cut to about half of the city of about 340,000.

Sewer lines were damaged and residents were being urged to conserve water supplies. Local resident Colleen Simpson told the Stuff website that many people had run out onto the streets in fear, while the mobile phone network was failing.

"Oh my God. There is a row of shops completely demolished right in front of me," Simpson said. Kevin O'Hanlon, from Mairehau in Christchurch, said: "Just unbelievable. I was awake to go to work and then just heard this massive noise and, boom, it was like the house got hit. It just started shaking. I've never felt anything like it."

The damage included structural harm to houses, broken glass and damaged bridges and vehicles. John Ristau, a seismologist at the government's GeoNet geological monitoring service, said the intensity was strong enough to cause structural damage to buildings.

© David Alexander/AP
Earthquake damage: buildings in Christchurch, 19 miles from the epi-centre, demonstrate the power of the tremors.
"It would most probably be the weaker buildings that have major damage to them," he said. An aftershock of magnitude 5.7 was felt at 4:53 a.m. local time, the USGS said, while local media said a series of shocks continued to roll across the city.

The quake was felt through much of New Zealand's South Island where Christchurch is located on its east coast, local media said. Christchurch International Airport, the main international gateway to the South Island, has been closed and rail movement in the South Island has been stopped while facilities are checked.

The magnitude was revised downwards from an initial estimate of 7.4, the USGS said. Although there was no evidence of a tsunami, the Pacific Tsunami Warning Centre said an earthquake of this magnitude could generate a local tsunami.

"Earthquakes of this size sometimes generate local tsunamis that can be destructive along coasts located within a hundred kilometres of the earthquake epicentre," the centre said. "Authorities in the region of the epicentre should be aware of this possibility and take appropriate action."

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From USGS:

Date-Time:
Friday, September 03, 2010 at 16:35:46 UTC

Saturday, September 04, 2010 at 04:35:46 AM at epicenter

Time of Earthquake in other Time Zones

Location:
43.375°S, 172.016°E

Depth:
12 km (7.5 miles) set by location program

Region:
SOUTH ISLAND OF NEW ZEALAND

Distances:
55 km (35 miles) WNW of Christchurch, New Zealand

185 km (115 miles) S of Westport, New Zealand

305 km (190 miles) NNE of Dunedin, New Zealand

325 km (200 miles) SW of WELLINGTON, New Zealand

Location Uncertainty:
horizontal +/- 11.2 km (7.0 miles); depth fixed by location program

Parameters:
NST= 98, Nph= 98, Dmin=86.7 km, Rmss=1.69 sec, Gp= 32°,
M-type=teleseismic moment magnitude (Mw), Version=8

Source:
USGS NEIC (WDCS-D)

Event ID:
us2010atbj

Source: Agence France-Presse