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Another 50 Christchurch buildings are likely to come down after the latest round of earthquakes hit the devastated city today.

Authorities have confirmed there has been no loss of life or serious injuries in this afternoon's major aftershocks, but are warning that thousands of residents should prepare for a night without power or water and expect further aftershocks.

Canterbury Earthquake Recovery Authority chief executive Roger Sutton says it's unclear at this stage how many more buildings have been damaged.

"More buildings have been seriously compromised by this. I'm guessing there's maybe another 50 buildings that will have to come down as a result of this. The Grand Chancellor is on more of a lean. We had surveyors in there when the second shake happened," he says.

Mr Sutton says the CBD is likely to remain closed for at least the next 24 hours.

Canterbury Police District Commander Superintendent Dave Cliff confirmed no one had been killed or seriously hurt following initial reports that people had been trapped in collapsed buildings, although at least half a dozen people have been taken to hospital with non-serious injuries.

Christchurch Mayor Bob Parker said the central city red zone, which was badly damaged in the February quake, was a "mess".

"There has been some significant additional damage inside the red zone, but we would expect that," he said.

Mr Parker said there also significant liquefaction in the eastern suburbs of the city and authorities were looking at setting up a welfare centre for people to stay through the night.

Engineers are just beginning to evaluate the damage caused to the city's already damaged waste water system, Mr Parker said.

Water pressure in the city has been lost following the aftershocks and residents have been asked to conserve water use.

Around 50,000 homes remain without power.

Mr Parker said people without those services should assume they will be without them overnight.

Authorities were looking at setting up an emergency operations centre outdoors.

Mr Cliff said heavy traffic had congested the city's roads.

"So if you don't need to travel again the message is please stay at home. The traffic is hampering emergency services."

Mr Parker reiterated that message.

"We must ask you to keep the roads as clear as you can simply because we need to get our services out on those roads. It is our lifeline as well."

Mr Cliff said there will be a high level of police patrols throughout the city tonight, and police resources could cope with more than 140 extra officers still in the city as a result of the February earthquake.

Mr Parker said that further aftershocks could be expected overnight but the trend being seen was for quakes of decreasing intensity.

"The great news is we have not lost lives.

"There have been some reports of some minor injuries but by and large everybody is fine and we need to think that way.

"We have to get through it again.

"There will be a few wobbles overnight but let's stay calm."

Schools and early childhood education services are being told to stay closed tomorrow.

The Ministry of Education says in these circumstances safety is paramount.

Schools in the Waimakariri and Selwyn districts are being told their board or management needs to make an assessment to open or close based on individual circumstances.

The quakes

The largest earthquake today, a 6.0, struck at about 2.20pm.

The first shake hit at 1pm and was a magnitude 5.5 quake, but there have been other minor earthquakes over the afternoon.

The first earthquake to hit Canterbury today struck near Darfield, but the remaining quakes have all been centred to the east of the city.

After the first 5.5 magnitude earthquake at 1pm, there was a 4.4 at 1.08pm, a 3.4 at 1.28pm, the 6.0 shake at 2.20pm, a 4.9 at 2.40pm and a 3.7 shake at 3.08pm.

The large quakes were felt as far away as Wellington and Invercargill, and caused further destruction in Christchurch.

Damage reports

Today's swarm of quakes has seen the scarred city suffer further damage:

* The Christchurch Airport terminal has reopened, but runway checks are continuing. Passengers should expect delays and contact their airlines for flight information.

* A bridge has reportedly come down following the magnitude 6.0 quake - believed to possibly be on Gayhurst Road, Avonside.

* The Old Waimakariri bridge, Moorhouse Ave overbridge, Gloucester/Gayhurst bridge and Anzac Ave bridge are all closed.

* The Merivale Mall has also been closed and the central police station has been evacuated.

* The historic Lyttelton Timeball Station - which suffered significant damage in the February 22 earthquake - has collapsed.

* Two people were rescued from the St John Church on Hereford and Madras streets, but they are not believed to be seriously injured.

* A unit on the corner of Stanmore and Worcester St collapsed, but rescue workers found no casualties.

* There have been reports of liquefaction bubbling up from the ground in the central Christchurch suburb of Richmond and the outer suburbs.

* Rocks have been seen falling from the hills in Sumner.

* Water has been reported pouring out of buildings on Stanmore Road.

* Lyttelton Port of Christchurch has sustained further damage in today's aftershocks. A full engineering assessment will be carried out over the next 12 hours and operations should commence at 7am tomorrow.

Power and phone

Power and phone services have been cut around Christchurch.

The earthquake has impacted both the cellphone and landline network. Telecom says it is assessing any potential network impact.

Telecom is also urging customers to text word messages, rather than pictures or video, and to limit voice calls to help conserve load on the network.

Telecom said there was some evidence of overloading on its network "as you would expect when there has been a decent shake".

Orion NZ says power has been cut to around 54,000 customers across Christchurch following the magnitude 6 earthquake.

Orion reports Spreydon, Sumner, Redcliffs, Heathcote, New Brighton, Dallington, Fendalton and St Albans have all been affected by power cuts.

Orion advises people in the eastern suburbs who have no power to prepare for a night without power.

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