Kiwis are coming to terms with the devastation of one of their proudest cities.

The 7.1 magnitude earthquake caused terror across Canterbury, damaged nearly 100 buildings and tore apart water pipes, sewerage, roads and footpaths.

Mayor Bob Parker said no decision had been reached on whether inner city Christchurch business would be permitted to open tomorrow.

An assessment on buildings in the city's central zone is expected to be completed today.

The water supply is back on for at least 85 percent of the city's residents, however issues with the supply may still force evacuations in Avonside, New Brighton and Brooklands.

Weather analyst Richard Green told Newstalk ZB the Canterbury region is set to face norwesterly winds between 60 and 130 kilometres an hour today. Winds of 80 kp/h have been reported at the epicentre in Darfield.

Civil Defence declared a state of emergency yesterday and ordered curfews. Police told residents to stay at home amid fears of aftershocks could cause more buildings to collapse.

Emergency services last night refused to rule out fatalities even as search and rescue teams, with dogs trained to search for human remains, flew to Christchurch.

Two men in their 50s were the only reported serious injuries last night. One man, hit by a collapsing chimney, was in a critical condition in hospital, while another was being treated for deep cuts.

Another Christchurch resident died of a heart attack as the quake struck. Doctors could not confirm whether the death was linked to the earthquake.

A massive clean-up was under way today as residents began returning to severely damaged homes. Treasury and the Earthquake Commission estimated the damage bill could exceed $2 billion.

Visiting the city where he was brought up, Prime Minister John Key said: "Parts of the city look like they've been put in a tumble dryer and given a damn good shake. You look at certain parts of the city and down town, it's essentially a ghost town. You can see utter devastation."

Key said it was an "absolute miracle" no one was killed. He said it was the worst disaster to hit the country since the earthquake that hit the West Coast town of Inangahua in 1968.

Key was touring the city centre with Mayor Parker when a building in Worcester St burst into flame when the gas and electricity were switched on at the same time.

Parker said: "Today in the face of this extraordinary event we have seen individual and collective stories of great courage and great compassion. They say it takes the worst to bring out the best, and Canterbury has shown what great people they are. People are pressing on and working together."

Resident Cam Gordon summed up the fear felt by people caught in the quake. "It was like a giant had picked up our house and was just shaking it, shaking and shaking."

Hadley Weir's story was typical of hundreds of people who narrowly avoided being crushed by falling debris.

Weir watched as a large pile of bricks toppled from a building on to his uninsured BMW in the city centre.

"It's lucky I wasn't already in the car. My friend had lost her handbag and was looking for it, otherwise we might have been," he said.

In the hours after the quake, looters raided a pharmacy and several liquor stores in the CBD.

Bealey Pharmacy proprietor Diane Hear said she found looters already outside her store when she arrived to survey damage. She called police who advised her to secure the building and try to protect it herself.

Hear said she scared the thugs off by telling them that police were on their way, even though she knew they weren't.

Hear said she had been terrified for her safety.

Betty's Liquor Store manager Steve Smith said thieves had punched a hole in the shop's reinforced front window before he arrived to clean up at 7am yesterday. He said the damage caused by looters had doubled his cost of repairs.

"I've been doing this job too long to be surprised by this sort of behaviour, but it's pretty gutting though, as I was hoping we were going to get through to daylight."

Firefighters used a turntable ladder to rescue a woman who was unable to escape from the seventh floor of a locked building in Colombo St.

Three people were rescued from lifts and at 5.40am a motorist drove in a 2m-3m deep hole in River Rd, Avonside, one of the worst affected areas.

Police Inspector Al Stewart said the CBD would remain locked down overnight and no licensed premises would be allowed to open.

Civil Defence controller Peter Mitchell said engineers would assess the damage in the central city today and decisions would be made on what buildings could open for business tomorrow. Almost 100 were thought to be damaged.

At the quake's epicentre in Darfield, 45km west of Christchurch, residents told of the terrifying ordeal.

"It was so bad out here it literally threw us out of bed," said Tim O'Donnell, from nearby Aylesbury. "The animals are all shaking too."

Aftershocks, some magnitude 5 or over, continued to rock the region throughout the day. The initial quake struck at 4.35am and was felt as far away as Taranaki.

Emergency calls overloaded the 111 system between 9am and 10am yesterday. Wellington shift inspector Mark Coleman said he understood it was caused by a Telecom fault.

Telecom head of external media Mark Watts said: "We responded to the very excessive demand on the system."

The company evacuated most of its staff from its Christchurch centre, diverting calls to a team in Palmerston North.

WeatherWatch.co.nz head weather analyst Philip Duncan said the gales expected today could make the disaster worse for everyone involved.

The rural community is coming to the city's aid with Fonterra and Federated Farmers organising three milk tankers containing 78,000 litres of drinking water to head to the city last night.

Reporting team: Anna Leask, Abby Gillies, Barry Clarke, Jamie Troughton, Laura Hall, Jarrod Booker, Philippa Williams, Celeste Gorrell Anstiss, Frances Morton with nzherald staff