A "severe'' magnitude 6.2 quake has damaged homes and closed roads in the lower North Island, toppling walls and chimneys and sending rockfalls across roads.
The quake struck 10km north of Castlepoint in Wairarapa, at a depth of 33km, at 3.52pm, GeoNet said.
Sara Page, GeoNet public information specialist at GNS Science, said GeoNet had received more than 6000 "felt" reports from the public by 4.30pm, with some reporting damage.
"As expected after a quake of this size, there have been multiple aftershocks, and these will continue for some time as the region settles," she said.
The Wairarapa is no stranger to large earthquakes, with two very damaging magnitude 7 quakes in 1942.
However, the region's last earthquake above magnitude 6 was in 1961.
Damage reports
There have been no reports of injuries but emergency services have reported damage to roads and buildings in the lower North Island.
Most of the damage was reported in the Wairarapa and Palmerston North areas.
Fire Service central communications shift manager Mike Wanoa said there were no reports of major damage so far, but firefighters were "extremely busy''.
"The earthquake has been reasonably major in the Masterton-Eketahuna area, so we're getting multiple calls to all sorts of things at the moment, but we're right in the middle of it now.''
There were reports of fires, alarm activations and lines down. A lot of the damage was in the Wairarapa and Palmerston North areas, Mr Wanoa said.
Inspector Mike Coleman of police central communications said there were reports of damage to houses in Eketahuna, including broken windows, collapsed walls and fallen chimneys.
The number of reports of damage remained unknown.
"Obviously some houses have been damaged,'' Mr Coleman said.
"Windows have been smashed and crockery has been thrown around the place - the usual sort of movement with earthquakes.''
Mr Coleman said there were rocks and debris on roads between Woodville and Taihape due to various slips.
The Manawatu Gorge road was down to one lane, while the road between Pahiatua and Palmerston North was closed.
Bridges and roads around Eketahuna were being checked, Mr Coleman said.
Motorists in the lower North Island were urged to take care.
A Wellington Free Ambulance spokesman said: "Wellington Free Ambulance has had no callouts as a result of the earthquake. However, we have gone into emergency management mode just to be safe.''
Tranz Metro said all train services in the region had been suspended due to the quake.
The New Zealand Transport Agency said teams were busy checking the road network for damage but everything seemed to be okay.
Power is out in Linton, south of Palmerston North.
A spokeswoman for the Earthquake Commission (EQC) said the agency was still gathering information on the quake and the volume of calls received.
One of the two giant eagles hanging from the roof of Wellington airport to promote the Hobbit trilogy did fall down as a result of the shaking.
The Weta Workshop eagles each weigh 2 tonnes, have a wingspan of 15m, and were suspended from the roof by eight cables.
Greg Thomas from Wellington Airport said one of the eagles slowly became detached during the quake and had come to rest on the floor.
He said it was still partly suspended, and no one was injured when it came down.
The quake had not caused any other damage at the airport. A runway inspection had been carried out and the airport had been cleared to continue operating.
No flights had been disrupted, he said.
'This one came with a bang'
Karen Monk, who is on a farm in Mauriceville, just north of Masterton, said the quake was "really violent''.
"My baby daughter was in her cot asleep and I managed to leap across the hall and grab her and leap outside onto the lawn,'' she said.
They had stayed outside for about half an hour while aftershocks rolled through.
Ms Monk said the quake was sudden and violent, compared to the usual rolling shakes.
"It was certainly the biggest we've had since we've been here.
"It was really sudden. Usually the earthquakes we feel up here, whether they're from north or south, they're more rolling and you start start with a gentle shake.
"This one just came with a bang, with massive jolting.''
She said the contents of the pantry had spilled onto the floor, shelves tipped over. Almost every room in the wooden villa had cracks in the walls.
"We're on a farm here and the animals don't normally react to quakes but the horses were running around for a good 10 minutes afterwards. The sheep are all huddled together. That's really unusual.''
An office worker in Masterton described the tremor as "a good quake - one of the best''.
"It was a roll rather than a jolt. It was not very long but it was long enough - it lasted about 20 seconds.''
Pam Lochore, wife of All Black great Sir Brian Lochore, said photographs had fallen off shelves in the couple's Masterton living room.
The shaking also caused water in the pool to "rock side to side'' and a "rugby ball went flying across the room''.
Raumati South resident Leigh Nichols was at her beachside bach when the quake hit.
"It was huge. The noise - it was like a train going along the track. It was so noisy, everything was just rattling.''
Mrs Nichols said a wine glass smashed and DVDs spilled to the floor. Her husband David clutched a wooden statue to prevent it tumbling over.
"It was the noise that got me, not the shaking. I just stood here. I don't get frightened, I'm fascinated.''
Asked how the quake compared to the big Seddon shakes in July last year, she said: "I think it was just as bad, at least.''
Mrs Nichols was about to head to her Raumati interior design store, Furnishing Affair, to check merchandise for damage.
"If it's only things, it's only things. But gosh it was big.''
In North Wairarapa crockery broke, fridge doors were flung open spilling food onto kitchen floors and disheartened homeowners described the aftermath as "a bloody mess''.
In Masterton initial reports showed there was little damage in shops although some crockery had been broken.
Anders Crofoot, owner of Castlepoint Station on the east coast of Wairarapa, said it was "the best shake we've had in 15 years''.
"Stuff off the shelves, stuff off walls, but nothing that we've come across that's too major,'' he said.
He said the shaking went on for about 40 seconds.
"I was up in the office and it was long enough to think about it and then get downstairs and outside and it was still going.''
He would now be checking the farm water supply for damage. "There's a high probability with some of these old pipes that there'll be a problem.''
Electricity retailer Powershop, which has its headquarters in Masterton, tweeted that it had evacuated its call centre following the earthquake.
The company said it would continue responding to email queries as best it could.
A DB Breweries spokeswoman said they had checked with staff at the Tui Brewery in Mangatainoka and there appeared to be no damage as a result of the quake.
A Fonterra spokeswoman said they were still checking into whether any damage had been caused at the company's Paihiatua dairy factory.
