Updated 8:11 p.m. ET
A powerful 7.0-magnitude earthquake struck much of New Zealand's South Island early Saturday and caused widespread damage, but there were just two reports of serious injuries. Looters broke into some damaged shops in Christchurch, police said.
CBS News Correspondent Ben Tracy reports that 75 percent of the city of nearly 400,000 people is without power, the hospital is running on a generator and countless water pipes have burst.
The quake, which hit 19 miles west of the southern city of Christchurch according to the state geological agency GNS Science, shook a wide area, with some residents saying buildings had collapsed and power was severed. No tsunami alert was issued.
GNS Science initially reported the quake as magnitude 7.4, but later downgraded it after re-examining quake records. The U.S. Geological Survey measured the quake at 7.0.
Despite being the same size as the devastating earthquake in Haiti that killed 230,000 people, the damage in New Zealand is much less due to better building codes and the time of day the quake hit, Tracy reports.
"People were home," Kate Hutton, a seismologist at the California Institute of Technology, told CBS News. "They weren't walking around in the streets past brick buildings."
Christchurch Mayor Bob Parker declared a state of emergency four hours after the quake rocked the region, warning people that continuing aftershocks could cause masonry to fall from damaged buildings.
"With these aftershocks rolling through - and we expect them to roll through for some days - quite clearly there's an ongoing danger, bits of glass that can still dislodge," Parker told CBS Radio News.
The emergency meant parts of the city would be closed off and some buildings closed as unsafe, he said.
Parker told CBS Radio News that officials are trying to inspect structures as quickly as possible.
"There's a lot of buildings that we need to inspect," said Parker. "We're looking at bringing in additional structional engineers."
A spokesman for Christchurch's fire service, Mike Bowden, said there haven't been any reports yet of people pinned underneath rubble although an unknown number of people are trapped in their houses and other buildings because of chimneys that fell, doors that jammed and entrances that became blocked, The Dominion Post, a New Zealand newspaper, reported.
The newspaper reports firefighters could only respond to "cases of life and death" because of the overwhelming demand for help.
Minister of Civil Defence John Carter said a state of civil emergency was declared as the quake was "a significant disaster," and army troops were on standby to assist.
Parker said the "sharp, vicious earthquake has caused significant damage in parts of the city ... with walls collapsed that have fallen into the streets."
Chimneys and walls had fallen from older buildings, with roads blocked, traffic lights out and power, gas and water supplies disrupted, he said.
"The fronts of at least five buildings in the central city have collapsed and rubble is strewn across many roads," Christchurch resident Angela Morgan told The Associated Press.
"Roads have subsided where water mains have broken and a lot of people evacuated in panic from seaside areas for fear of a tsunami," she said, adding that "there is quite significant damage, really, with reports that some people were trapped in damaged houses."
Christchurch Hospital said it had treated two men with serious injuries and a number of people with minor injuries.
One was hit by a falling chimney and was in serious condition in intensive care, while a second was badly cut by glass, hospital spokeswoman Michele Hider said.
Christchurch police reported road damage in parts of the city, with a series of sharp aftershocks rocking the area. Police officers cordoned off some streets where rubble was strewn about. Video showed parked cars crushed by heaps of fallen bricks, and buckled roads.
"There is considerable damage in the central city and we've also had reports of looting, just shop windows broken and easy picking of displays," Police Inspector Mike Coleman told New Zealand's National Radio.
Police Inspector Alf Stewart told the radio that some people had been arrested for looting.
"We have some reports of people smashing (storefront) windows and trying to grab some property that is not theirs ... we've got police on the streets and we're dealing with that," he said.
Radio New Zealand reports listeners were reporting particularly strong effects in Christchurch. One said his house "turned upside down" with crockery breaking. Sewer lines and water pipes have ruptured.
The Christchurch newspaper The Press reports several aftershocks have occurred.
Suburban dweller Mark O'Connell said his house was full of smashed glass, food tossed from shelves, with sets of drawers, TVs and computers tipped over.
"She was a beauty, we were thrown from wall to wall as we tried to escape down the stairs to get to safety," he told the AP. "It was pitch black (with the power cut) and we walked through smashed glass everywhere on the floor."
The quake hit at 4:35 a.m. local time (12:35 p.m. ET Friday) shaking thousands of residents awake, New Zealand's National Radio reported.
Civil defense agency spokesman David Millar said at least six bridges in the region had been badly damaged, while the historic Empire hotel in the port town of Lyttelton was "very unstable" and in danger of collapse. Roads, shops and other buildings in rural towns around Christchurch had also suffered damage, with some shop fronts knocked down in the jolt.
Inspector Coleman said residents of the city's low-lying eastern suburbs had been advised to be ready to evacuate their properties, after power, gas, sewerage and water systems were cut by the quake.
Resident Colleen Simpson said panicked residents ran into the street in their pajamas. Some buildings had collapsed, there was no power, and the mobile telephone network had failed.
"Oh my God. There is a row of shops completely demolished right in front of me," Simpson told the Stuff news Web site.
Another person from Christchurch, Kevin O'Hanlon, said the jolt was extremely powerful.
"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," he told the news Web site.
Christchurch International Airport was closed after the quake as a precaution, as experts prepared to check the runways and terminal buildings, a spokesman said.
The Pacific Tsunami Warning Center said "no destructive widespread tsunami threat existed, based on historical earthquake and tsunami data."
New Zealand sits above an area of the Earth's crust where two tectonic plates collide. The country records more than 14,000 earthquakes a year - but only about 150 are felt by residents. Fewer than 10 a year do any damage.