A state of emergency was declared in New Zealand\'s second largest city Christchurch after a powerful 7.0 magnitude earthquake struck before dawn on Saturday, causing widespread damage.

The location of a strong earthquake which hit New Zealand. A powerful 7.0 magnitude earthquake rocked New Zealand\'s second largest city Christchurch just before dawn Saturday, causing widespread damage and panic among residents, but no serious injuries.

Frightened residents fled from their homes to find roads blocked by the facades of buildings which crashed down and crushed parked vehicles, while roads were littered with glass.

There was structural damage to buildings throughout the city of 340,000 people, with gas leaks, ruptured water and sewerage mains, collapsed bridges and cuts to electricity supplies.

Only two people were seriously injured, but Civil Defence officials said that had the quake hit in daylight, when there would have been thousands of people on the streets, the toll could have been much worse.

Christchurch mayor Bob Parker said he was "horrified by the amount of damage" which daylight showed was considerably worse than first thought.

"We\'ve decided to declare the state of emergency in the city. It just makes it a bit easier for us now to move people out of buildings if necessary, close streets down," Parker announced on national radio.

The quake, initially recorded at a magnitude of 7.4, struck at 04:35 am (1635 GMT Friday) and was centered at a depth of 16.1 kilometres (10.0 miles) some 30 kilometres (19 miles) west of Christchurch, the US Geological Survey said.

"Oh my God. There is a row of shops completely demolished right in front of me," local resident Colleen Simpson told the Stuff website, adding that many people had run out onto the streets in fear.

Christchurch Hospital spokeswoman Michele Hider said two men in their 50s were seriously injured -- one was hit by a falling chimney and the other was cut by falling glass.

Several people were treated for minor injuries from objects falling in their homes, while hospitals had additional doctors on standby because of the intensity of the quake and the extent of the damage.

Police closed the centre of the city as looters targeted damaged shops, police Inspector Mike Coleman said.

"There\'s considerable damage there, and we\'ve already had reports of looting. Shop windows are broken and obviously it\'s easy pickings for displays and things."

Coleman said that with the extensive damage, people were being urged to stay at home.

"We\'ve got considerable road damage, there\'s gas leaks, there\'s been damaged water pipes, we\'ve got sewage in houses and quite a lot of power lines and power poles down. It\'s very unsafe to be out and about."

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, while electricity supplies were cut to about half of the city.

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."

John Ristau, a seismologist at the government\'s GeoNet geological monitoring service, said the intensity was strong enough to cause structural damage to buildings.

"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 1653 GMT (0453 local time), the USGS said.

Mayor Parker said the continuing aftershocks meant there was a danger of further damage, while people were at risk from falling glass.

Parker said he was in bed when the first quake struck and he was "absolutely scared. I\'ve never felt anything like it and I\'ve experienced, like most Kiwis, a number of good shakes."

The quake was felt throughout the South Island and the lower North Island.

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.