LATEST: Central New Zealand has been hit by a severe magnitude 6.5 earthquake, which was felt in Hamilton and the wider Waikato.
It was centered in the Cook Strait, 20 kilometres east of Seddon, at a depth of 17 kilometres. It struck at 5.09pm.
The shaking was also felt in Hamilton, where it gently swayed for close to a minute.
Patients at Waikato Hospital felt their beds move and Hamilton residents reported blinds banging against windows and televisions, couches and light fixtures swaying.
At least two people have been reported as injured - one person in Kapiti and another who was hit by a falling television in Wellington.
Aftershocks have continued throughout the night. One "strong" aftershock at 8:27pm was magnitude 5.3 at a depth of only 14 kilometres, according to Geonet.
It is the latest in a sequence of major earthquakes in Wellington and wider areas around central New Zealand since Thursday.
There has been damage to buildings and roads in Wellington and Malborough, and several supermarkets have closed as staff clean up food items that have fallen from shelves.
On Facebook people said it was felt right across the Waikato, including Tokoroa, Te Kuiti, Raglan, Ngaruawahia and Huntly.
Te Kowhai resident Gail Henshaw said: "...our rocking chairs started swaying backwards and forwards and even side to side."
Joyce Goodwin said: "Having a bath and reading a book in Dinsdale, felt a bit weird and the water started going sideways in the bath and the towels were swaying on the rail."
A fire service spokeswoman said the phone had been ringing off the hook in Wellington, with power lines down, people trapped in lifts and multiple sprinkler activations in city buildings.
"We've had reports of damage to some buildings down town. We've got power lines that are coming down."
Every fire truck had been sent to jobs, she said: "We've got all of Wellington out now. And we've got jobs waiting to be addressed. We are prioritising jobs."
There have been no reports of earthquake-related emergency callouts in the Waikato.
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.
GNS Science research seismologist Stephen Bannister said a magnitude 6.5 earthquake releases energy equivalent to 100 nuclear bombs of the size which devastated Hiroshima.
There had been more than 230 earthquakes since Friday in the area, with about 15 above magnitude 4.