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This afternoon's 4.5 magnitude aftershock has pushed a number of damaged Christchurch buildings over the edge.
The 12 story Radio Network-Newstalk ZB building in Worcester Street is one that officials have ordered be evacuated after the tremor at 12.35pm.
It had sustained some damage during Saturday's quake, and the aftershock has made some of the cracks worse.
Radio Network stations will continue to broadcast from back up facilities.
Lucky escape
Two people also escaped unharmed after running from an unstable brick building which showed signs of collapsing during the same strong aftershock this afternoon.
The owners of vintage store La Boutique, mother and son Rose and Myles Lennon, were in the brick building on the corner of Westminster and Cranford Streets that houses the shop and other retail outlets when a 4.5 magnitude aftershock hit at around 12.35pm.
Ms Lennon said she was in the shop "grabbing whatever I could" when the shaking began.
"I forgot everything else and just ran for it," she says.
"There were huge cracks down the walls and there was dust and water coming down. The whole place was shaking. It was scary."
Myles says "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 and the building, in the suburb of St Albans, is now being destroyed.
Inspector John Price of Christchurch police said safety was paramount and people should steer clear of the building.
"Cordons may vary depending on the weather conditions and possible aftershocks. As civil engineers and USR teams move through the city, further buildings may be deemed to be at risk," he said.
Mr Price also issued a warning to the "small number of people interfering with taped off areas and removing safety cones.
"Removal prevents the protection and safety of everyone."
Aftershocks rock region
The incident followed news of a significant aftershock which reportedly knocked out the lights at Christchurch Airport.
According to GeoNet, there have been 18 significant aftershocks today, ranging in magnitude from 3.5 to 4.8. The latest, at 3.54pm, was a 3.7 magnitude shock centred at a focal depth of 20km depth which struck near 20km west of Christchurch.
A 3.5 magnitude slightly shallower shock centred in the same spot was felt at 12.18pm. The largest aftershock today was at 4.06am - a 4.8 magnitude, 10km deep quake centred 10km south of Coalgate, a town west of Darfield.
Experts say while aftershocks may continue for weeks, they will diminish in size and frequency and the worst are likely to be over by today.
Demolition begins
Despite the aftershocks, contractors have begun tearing down dangerous buildings half destroyed in Saturday's 7.1 magnitude quake.
Diggers on Victoria and Bealey Street in the city are tearing down what is left of a two storey food market that used to stand opposite Knox Church.
Christchurch's Central Business District is still cordoned off but the extent of the cordon has been reduced overnight.
People are still being asked to stay away while assessments are done.
More than 500 buildings in the city are badly damaged, 90 significantly which may need to be demolished.
It's estimated just under 4,000 homes are without power - 98 per cent of homes have had power restored.
Parts of CBD could be closed for weeks
Authorities say some parts of the Christchurch central business district could be off-limits for weeks until damaged buildings are demolished or declared safe.
Christchurch City Council staff are evaluating damage to buildings and colour-coding them - green for sound, red for dangerous, and yellow to indicate structural problems.
Business owners in the central city will be allowed to check their stores today but will not be allowed to open for business.
Water and sewage a major concern
About 60 streets across Christchurch are still without water this morning as aftershocks continue to shake the city after Saturday's earthquake.
To date, almost a third of all jobs recorded relating to water and wastewater have been resolved and teams are working around the clock to restore water supply to the city.
Christchurch residents are being told to boil their water. KiwiRail has shunted in 14 milk tankers carrying 20,000 litres of water each.
Teams will be working today with cameras to inspect pipes to identify the highest priority repairs.
Christchurch mayor Bob Parker says a number of cases of gastroenteritis have been reported in the city, according to Newstalk ZB.
Sewerage pipes as well as water pipes have been leaking. All schools in the Christchurch, Waimakariri and Selwyn districts are closed until at least Wednesday.
In Rolleston the local council is warning residents that their water supply has been contaminated.
A spokeswoman said an update this afternoon would advise people where to go for water.
She said everyone should be treating their water as contaminated until told otherwise.
"The contamination is due to cracks and leaks in the waste water pipes," she said.
About 180 staff worked on water supply and waste water last night.
0800 helpline
The number of people calling the Government's helpline has more than doubled since yesterday afternoon, Social Development Minister Paula Bennett says.
More than 2500 people have now called the 0800779997 helpline set up to offer advice and referrals for other services.
Just over 1000 had called by yesterday afternoon.
Ms Bennett said five Work and Income offices were confirmed as safe and are open today in Christchurch to provide support.
Four other offices in Canterbury remained closed due to structural damage.
Benefit and superannuation payments will continue without disruption, Ms Bennett said.
Govt to announce earthquake response this afternoon
Cabinet will today meet to get an early overview of the damage caused by the Canterbury earthquake.
Prime Minister John Key said the bill outside private insurance and the Earthquake Commission funding would be large.
Christchurch City Council has extended the state of emergency until midday Wednesday.
Mr Key surveyed damage caused by the 7.1 magnitude quake on Saturday afternoon and said it was an eerie feeling walking around Christchurch and observing families as they took in the scale of the disaster.
"Also you could see they were feeling quite stressed from the night before and a little fearful of the aftershocks that they knew were coming," he told TVNZ's Breakfast programme.
"I know lots of families slept in the middle of the lounge on the Saturday night wanting to be together."
He said Cabinet would today get an update on all the different issues being presented. "And there are some practical micro things happening, for instance, the Ministry of Social Development are contacting all their elderly clients to make sure that people are okay. ACC are contacting those with serious injuries..."
He said there was plenty of damage to infrastructure such as roading and wastewater, and the burden of repairing it would need to be spread.
"It was previously paid for by the ratepayers of the Canterbury region, and quite frankly the Government is going to have to step up and I think wear a majority of that cost, simply because if we don't do that the people of Canterbury have to pay, because they need that infrastructure."
Mr Key said a lot of the cost of damage to buildings would be met by the Earthquake Commission - up to $100,000 per building and $20,000 for contents - and private insurance.
However, there were cases where some had heavy damage to their homes yet didn't have private insurance.
Such situations presented a difficult issue and would be part of the Cabinet's discussions today, Mr Key said.
He said from what he had seen, Civil Defence had responded well to the crisis.
"By the time I got to Christchurch it was a very slick operation."
Claims lodged with Earthquake Commission
Late last night, 4164 householders had already lodged claims with the Earthquake Commission, and the total is predicted to rise to at least 100,000.
Ngai Tahu marae could be used to house families too scared to sleep in their own homes.
Te Tai Tonga electorate MP Rahui Katene said she was looking into several inner-city marae which have mattresses and an attached whare kai (eating house).
"We need to get people feeling comfortable and safe because they just don't feel safe in their homes," she said.
Ms Katene said Rehua Marae, right in the middle of town, would have been ideal but a tangi was being held there.
She said she knew of a family of six that were looking for temporary shelter and could no longer stay with whanau who were short of space.
Ms Katene said she had also visited Tuahiwi Marae, near Kaiapoi.
"It looked fine but [I've been told] there are cracks in the wall and it has moved," she said.
All non-essential procedures at Christchurch Hospital have been cancelled, as have jury trials due to start today.
KiwiRail this morning said that all rail services in the Christchurch area were likely to be restored by Tuesday.
It said the Main South Line south from Christchurch had already reopened with speed restrictions in place. The Midland Line west of Otira is open and the line between Otira and Christchurch expected to reopen this afternoon.
The Main North Line was expected to reopen tomorrow.
* 500+ Buildings damaged
* 90+ CBD buildings damaged
* Estimated cost of damage: $2 billion
* Magnitude of Saturday's quake: 7.1
* 58 Aftershocks
* 245 Residents housed in welfare centres
* 15 per cent of Christchurch homes still without water
* 300,000 litres of water transported to Christchurch by rail yesterday
* Distance of epicentre from Christchurch central: 40km
- NZ HERALD STAFF, NZPA
Map: Christchurch earthquake damage
KEY
Red marker: Epicentre
Blue markers: General damage
Green markers: Public service advice and information
Yellow markers: Locations of welfare centres
Purple markers: Damage to historic buildings
View Christchurch earthquake in a larger map
