At least 500 buildings, including 90 properties in downtown Christchurch, have been designated as destroyed in the quake that struck at 4:35 a.m. Saturday (1635 GMT Friday) near the South Island city of 400,000 people. But most other buildings sustained only minor damage.
Only two serious injuries were reported as the quake shattered glass and chimneys and walls of older buildings crumbled to the ground. The prime minister said it was a miracle no one was killed.
Power was cut across the region, roads were blocked by debris, and gas and water supplies were disrupted, Christchurch Mayor Bob Parker said. He warned continuing aftershocks could cause masonry to fall from damaged buildings, as could gale force winds due to buffet the region Sunday.
Canterbury University geology professor Mark Quigley said what "looks to us that it could be a new fault" had ripped across the earth and pushed some surface areas up about three feet (a meter). The quake was caused by the ongoing collision between the Pacific and Australian tectonic plates, he said.
"One side of the earth has lurched to the right ... up to 11 feet (3.5 meters) and in some places been thrust up," Quigley told National Radio.
"The long linear fracture on the earth's surface does things like break apart houses, break apart roads. We went and saw two houses that were completely snapped in half by the earthquake," he said.
Roger Bates, whose dairy farm at Darfield was close to the quake's epicenter, said the new fault line had ripped up the surface across his land.
"The whole dairy farm is like the sea now, with real (soil) waves right across the dairy farm. We don't have physical holes (but) where the fault goes through it's been raised a meter or meter and a half (3 to 5 feet)," he told National Radio.
"Trouble is, I've lost two meters (6 feet) of land off my boundary," he added.
Experts said the low number of injuries in the powerful quake reflects the country's strict building codes.
"New Zealand has very good building codes ... (that) mean the buildings are strong compared with, say, Haiti," which suffered widespread damage in a magnitude-7.0 quake this year, earth sciences professor Martha Savage told The Associated Press.
"It's about the same size (quake) as Haiti, but the damage is so much less. Though chimneys and some older facades came down, the structures are well built," said Savage, a professor at the School of Geography, Environment and Earth Sciences at Victoria University in the capital, Wellington.
"Thank God for earthquake strengthening 10 years ago," Anglican Dean of Christchurch, Rev. Peter Beck, told TV One News on Sunday.
Euan Smith, professor of Geophysics at Victoria University, said the fact that there "were no fatalities ... it's quite remarkable."
Experts were speculating the very soft soils of Christchurch had "acted like a shock absorber over a short period ... doing less damage to smaller buildings. They will dissipate earthquake energy if they're thick enough," he told The AP.
Christchurch fire service spokesman Mike Bowden said a number of people had been trapped in buildings by fallen chimneys and blocked entrances, but there were no reports of people pinned under rubble.
Rescue teams with sniffer dogs were continuing to check premises.
State geological agency GNS Science reported more than 40 aftershocks in the 24 hours following the quake, ranging in strength from magnitude 3.7 to 5.4.
A state of emergency was declared and army troops were on standby to assist after the quake, which was centered 19 miles (30 kilometers) west of Christchurch, according to GNS Science. No tsunami alert was issued.
Prime Minister John Key, who flew to Christchurch to inspect the damage, said it was "an absolute miracle" that no one had died.
He warned it could be months before the full extent of the damage was known, but said initial assessments suggested it could cost at least 2 billion New Zealand dollars ($1.4 billion) to repair.
"There is a major rebuild job here in Christchurch ... and people are terrified at what took place," he said Sunday.
Civil Defense officials lifted a curfew on the central city area Sunday morning, while police commander Superintendent Dave Cliff said only two arrests had been made overnight for breaching the security cordon set up to prevent people being injured by falling masonry.
"Some parts of the city are very dangerous" because of unsafe buildings he said, and a cordon would remain in place as gale force winds hit the region during the day.
Up to 90 extra police officers had flown in to Christchurch to help, and troops were likely to join the recovery effort on Monday, Parker said.
About 250 people had taken refuge overnight Sunday in accommodation centers at schools in suburban areas to house people forced out of their damaged homes, civil defense spokesman Murray Sinclair said.
Minister of Civil Defense John Carter said there was "a lot of damage to our key infrastructure ... water, waste water systems."
Christchurch Hospital said it had treated two men with serious injuries and a number of people with minor injuries.
One man was hit by a falling chimney and was in serious condition, while a second was badly cut by glass, hospital spokeswoman Michele Hider said.
Christchurch police reported road damage in parts of the city and cordoned off some streets where rubble was strewn about. Parked cars were crushed by heaps of fallen bricks, and roads buckled.
Civil defense agency spokesman David Millar said at least six bridges had been badly damaged and the historic Empire hotel in the port town of Lyttelton was "very unstable" and in danger of collapse. Several wharves at the port were damaged.
People in the city's low-lying eastern suburbs were told to be ready to evacuate after power, gas, sewage and water systems were cut by the quake, Police Inspector Mike Coleman said.
Kiwirail rail transport group spokesman Kevin Ramshaw said 13 trains, mostly freight, had been halted, with some damage confirmed to lines north of Christchurch.
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.
New Zealand's last major earthquake registered magnitude 7.8 and hit South Island's Fiordland region on July 16, 2009, moving the southern tip of the country 12 inches (30 centimeters) closer to Australia, seismologist Ken Gledhill said at the time.