Severe dispruption is expected in Wellington following a magnitude 6.5 earthquake that damaged buildings, cut power, trapped people in lifts and injuried at least two.
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GeoNet said the 6.5 magnitude earthquake was centred in the Cook Strait, 20 kilometres east of Seddon at a depth of 17 kilometres. It struck at 5.09pm.
The Pacific Tsunami Center in Hawaii said the quake did not generate a tsunami, but a number of smaller quakes have struck since - the latest, a 4.4 magnitude 25km east of Seddon at 8.27pm, followed closely by a 5.1 magnitude near Hanmer Springs.
A spokesman for Civil Defence Minister Nikki Kaye confirmed a civil defence emergency had not been declared, but an emergency centre had been set up in Thorndon.
Earlier reports of sinkholes in Featherston St had been retracted by police.
At least two people have been reported as injured - one person in Kapiti and another who was hit by a falling television in Wellington.
A spokesman for Wellington Free Ambulance said they received a number of calls following the quake.
"We had one guy knocked out by a TV falling on him. That was at the Soho Apartments in Taranaki St. He was a male in his 40s and was taken to Wellington Hospital."
Major commuter chaos was being predicted for Wellington tomorrow morning. All train services were cancelled without any buses to replace them.
Wellington CBD workers are being urged to hold-off heading into work till noon tomorrow to give landlords and engineers time to assess quake-damaged buildings.
Wellington Region Civil Defence Controller, Bruce Pepperell, said people should check with work before heading into the CBD and if they did come in, stay away from quake-damaged facades.
"I am worried about some of the facades. It would only take a little shake to move some of that stuff and it could end in tragedy."
KiwiRail spokeswoman Sophie Lee said there had been no reports of damage to the tracks this evening. But because much of the assessment was done after dark, the call had been made to do a more thorough check in the morning, she said.
"Given the seriousness of the aftershocks and the fact that (the inspection) is taking a lot of time, we've decided to take every precaution."
No buses were available on such short notice so rail commuters would need to make alternative arrangements, she said.
KiwiRail was hopeful of having at least some services back up and running by midday on Monday.
There had been extensive reports of damage to buildings in the capital, but so far most of it minor.
Pepperell said engineers were urgently assessing the Mercure Hotel on Willis St this evening after it sustained damage if the quake.
He said he understood the hotel had sunk by about 5cm on one side and parts of the floor were uneven.
A section of ceiling collapsed on the third floor of the community health building at Hutt Hospital. Four staff members were evacuated.
Police spokesman Inspector Marty Parker said buildings in the city were being evacuated after structural damage was discovered.
Road blocks were also in place around the Mercure, he said.
A fire service spokeswoman said people had to be rescued from lifts in Molesworth and Brandon Streets, and in Thorndon, mainly in apartment blocks.
A number of glass windows across the city had also smashed, and cracks had appeared in many buildings.
Wellington Maritime Police senior launch master Barry Hart said a piece of previously reclaimed land along the industrial part of the waterfront had subsided into the sea, taking with it at least one shipping container.
"The land has actually subsided at least a couple of metres... into the sea. One shipping container has gone into the water."
He said the nearby container cranes were still standing and appeared not to have sustained damage. The ferry terminals also appeared to have survived unscathed, he said.
Infrastructure across the central and lower North Island, and the top of the South Island had ground to a halt.
There was a slip on Highway 1 south of Seddon, which was believed to be as a result of the quake.
Marlborough Roads general manager Frank Porter was not sure of the exact location. But a team had been sent out.
It was not yet known whether the highway would be closed.
Emergencies Services manager at the Council, John Foley, said power was out around the region, and Marlborough Lines were checking to see how long people would be without power.
Phone lines jammed in the top of the South Island and bottom of the North Island immediately after the large quake struck as people tried to call family and friends, a Telecom spokeswoman said.
Both the mobile network and the landline network were overloaded for 15 to 20 minutes.
"There was a spike in traffic straight after the quake hit, which is as we would expect - everyone getting on the phone to make sure their family is OK.
"To the best of our knowledge there's no network damage."
People should send text messages, instead of calling, to ensure emergency calls can get through, the spokeswoman said.
Vodafone customers were also affected when nine mobile sites went down immediately after the large quake.
Sites in Marlborough were affected by power outages and two Wellington sites lost coverage, a spokeswoman said.
"Some customers may have had problems with calls and texts following the quake - issues compounded by overloading on the network, rather than damage."
The network was now stable and all mobile cell sites had been restored.
"Our guys are just making sure now that staff are OK, buildings are OK and that the network is stable."
Prime Minister John Key was not in the capital but his spokesman said his thoughts were with quake-hit regions.
"This will be a frightening time for people in areas where the quakes are most felt, and the Prime Minister's thoughts are with them at this time," the spokesman said.
Key was being kept informed on events.
"No tsunami warning for the region has been issued. However, the Wellington City and Hutt City Regional Emergency Management Offices are activating to coordinate any response at a local level," the spokesman said.
"At this stage, the Prime Minister will be returning to Wellington on Monday morning, as planned."
A Kiwirail spokeswoman said services from Otaki in the North Island to Kaikoura had been suspended until further notice.
There could be some disruption to freight services between Picton and Kaikoura, while an inspection of the tracks, bridges and tunnels was done, the spokeswoman said.
A spokesman for the NZ Transport Agency said an initial damage report of state highways in the quake zone was done and no damage or blockages were found.
The agency would carry out more detailed inspections tomorrow, he said.
The 6.5 magnitude quake was likely linked to a fault in the Cook Strait capable of generating far more severe shaking, GNS Science said.
Dr Kelvin Berryman, GNS Science director of Natural Hazards, said the severe shaking over the past three days was probably linked to one of several faults capable of generating shakes of magnitude 7.0 or more.
The most likely candidate was the Needle fault, although the location of the quakes over the past three days did not quite match up.
He said a larger quake was unlikely but the swarm that kicked off on Friday morning was not following the normal aftershock pattern, in which the tremors became progressively less severe.
This afternoon's 6.5 magnitude shake, the biggest in the latest swarm, meant the shaking was not following the usual pattern, he said.
GNS should have a clearer idea of the probability of another big, or even bigger, quake by tomorrow, he said.
The Earthquake Commission announced earlier this month that they had renegotiated $3.25bn in reinsurance cover.
Chief Executive Ian Simpson said at the time that EQC has sufficient cover to meet the costs of a "significant' disaster.
If there were a sequence of events, as in Canterbury, it would have up to $6.5bn in cover. A spokesman for EQC minister Gerry Brownlee said EQC had "ample to cover any future event."
* Police advise that their earlier reports of sinkholes in Featherston St are not correct.