A mother and son had to flee their crumbling store during a powerful aftershock in Christchurch yesterday, and other business owners were heartbroken after seeing their wrecked properties for the first time.

"I forgot everything else and just ran for it," said Rose Lennon, who owned secondhand clothing store La Boutique with son Myles.

"There were huge cracks down the walls and there was dust and water coming down. The whole place was shaking. It was scary."

The pair were in the brick building on the corner of Westminster and Cranford Sts in St Albans when the 4.5-magnitude aftershock hit about 12.35pm.

Ms Lennon said she was in the shop "grabbing whatever I could" when the shaking began.

Myles Lennon said it was "really, really intense. I had a real sense of urgency come over just to get out."

Emergency services were called to the scene. The building was condemned and demolition soon got under way.

"It's just heartbreaking," said Ms Lennon. "Today I should be serving customers. Instead I am sitting on the street watching it being ripped down."

The lucky escape highlighted the dangers severely damaged buildings still pose to Christchurch residents and business owners after Saturday's earthquake.

The Government says about 100,000 of the 160,000 homes in the Christchurch, Selwyn and Waimakariri areas were damaged in the 7.1-magnitude shake.

Last night, more residents were moving valuables out of Seabreeze Close, in the suburb of Bexley.

Every house on the street - featured in the Herald yesterday - has been deemed a write-off by residents, and they were racing to remove household goods amid rumours of an impending evacuation.

The street is still without power and water, and mounds of sand and mud cover the front lawns and driveways of the properties.

Christchurch remains in a state of emergency today. The city council is planning to re-assess the situation at midday tomorrow.

Last night, police said engineers had surveyed 550 buildings in the city centre.

Five per cent were deemed unstable and unable to be entered, 16 per cent could be entered to check for damage, and the rest were sound.

A police cordon was still in place around the city centre last night, and the area bounded by Armagh, St Asaph, Durham, Tennyson and Madras Sts was off-limits.

Business owners had their first chance yesterday to see the multimillion-dollar damage to their properties and get inside their premises to salvage what they could.

But central-city workers were kept outside barricades manned by police and soldiers from Burnham military camp, south of Christchurch, who have been called in to help police.

Central City Business Association manager Paul Lonsdale said the loss of trading was the last thing the businesses needed after a tough winter.

Many did not know if their insurance would cover their losses.

"For some who have been struggling, it may be just a little bit too much for them."

Roger Kelso was allowed past the barricades yesterday to check on the jewellery store he has owned for 40 years, and found it surrounded by bricks, concrete and steel from the collapsed facade on the storey above.

The sight left him "pretty devastated".

"It's something I never imagined would happen. But it's happened and we've got to get on. We'll have to find other premises. You've got to look to the future."

Mr Kelso does not know what he will find inside his premises when the debris is cleared.

But he is pleased the quake did not strike while the store was open and staff and customers were in it.

"All the damage in the world you can take, but one death is something different."

Craig Webster was yesterday inspecting 15 buildings he owns in the central city.

Four were seriously damaged, and one century-old seven-level building with about 15 tenants was "looking very sick".

"These are heritage buildings, and a lot of them are going to be gone," Mr Webster said.

"We are insured, but we are unsure how it's all going to work out. We understand the loss-of-rents [insurance] only lasts for 12 months, so what do we do after that?"

About 20 aftershocks rattled Christchurch yesterday.

But officials are worried that the biggest has not yet struck, and schools will remain closed until tomorrow as Civil Defence and Ministry of Education staff assess the safety of buildings.

Trials in Christchurch courts have been postponed, because court staff expect those involved will be unable to attend.

But public transport resumes today and bus services will run outside the city centre.

When NZS.com director Mark Rocket arrived at his flooded office with employees to Heartbreak

in the rubble

for owners

salvage what they could, water was dripping onto desks and computers from broken sprinkler pipes.

"It's horrific. I couldn't believe it," Mr Rocket said. "But there was no structural damage, at least, so we could get in to pick up the pieces.

"It'll take weeks, probably months, to get back to normal."

He said the company, a NZ internet search provider, would continue operating on back-up servers, with employees working from home.

"I just don't think about it too much," Mr Rocket said. "In a few months I'll reflect on it. Right now it's just a matter of doing what you can."

The company's chief executive, Gary Jensen, said dealing with personal and work emergencies after the quake had been difficult.

"I was busy shovelling at my mother-in-law's house, which was completely destroyed, and now I'm here."

Rod Hair's 130-year-old two-storey building lost its facade, and bricks from the building next door were piled on the roof.

"So we are trying to get these bricks off and put tarpaulins down ... If it rains, the water will pour through."

R&R Sport manager Graeme Allen was clearing rubble from his crumbling frontage.

Broken glass and collapsed balconies made the situation look dire, he said, but "internally, it's pretty good".

100,000 - Number of homes damaged by Saturday's quake
160,000 - Number of homes in the region
431 - Homes likely to be demolished
16,000 - Number of years since faultline last ruptured
$5 million - Government donation to the mayoral fund
3500 - Homes still without power