A powerful 5.8 magnitude earthquake was felt by more than 37,000 people across the length of New Zealand, sending many ducking for cover as the "long and rolling" tremors lasted 30 seconds.

There have since been at least 45 aftershocks before 11am, with the strongest measuring magnitude 4.4.

The initial earthquake struck 30km northwest of Levin at a depth of 37km at 7.53am this morning.

It was felt as far north as Auckland and near the bottom of the South Island, according to GeoNet.

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Newstalk ZB's Adam Cooper said it was a "very big quake".

"A rattler, went on for a long time," he said.

More than 37,000 people had reported feeling the quake by 8am. Almost 100 said it felt "severe" while 10 said it felt "extreme."

Originally GeoNet said it was a 5.9 magnitude quake, and later revised that to 5.8.

Jacinda Ardern was live on television this morning when the earthquake struck.

"We're just having a bit of an earthquake here," the PM said to Newshub host Ryan Bridge as the screen began to shake.

"Quite a decent shake here," she continued as the Covid-themed backdrops quivered behind her.

At least 45 aftershocks have occurred in the area as well.

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All have been categorised as "light" or "weak" earthquakes on the GeoNet website. The strongest reported was magnitude 4.4, 25 km north-west of Levin and 39km deep. It hit at 10.44am.

All Metlink train services are being held at stations following the quake. At 8.30am it said train services remain suspended across the rail network and to expect significant delays.

"During this time we are trying to source buses however please be advised that bus replacements will be limited," Metlink said.

"Limited bus replacements along the Hutt Valley and Kapiti Line," Metlink tweeted. "We advise to use alternative transport."

Wellingtonian Mike Cagney had just pulled up to an intersection near the Wellington railway station when he thought "Why the hell is my car rocking?"

He initially thought there was something wrong with his car or it was being buffeted by wind.

"It was jumping quite strongly and it was like holy cow - it was only later I realised it was an earthquake," he said.

National MP Amy Adams was in a meeting at Parliament when it started to shake - causing all five people in the room to get under the table.

"We sort of all looked at each other and then everyone was getting under the table."

She did not expect it to last as long as it did - about 30 seconds, she guessed.

"It was a decent length and it certainly rolled around."

No one was hurt, she said, and nothing in the room had fallen.

Asked whether new National Party leader Todd Muller was in the meeting at the time, she said no.

Adams said being from Christchurch, she had experienced and lived through "thousands" of earthquakes and dubbed that one "pretty strong".

It was longer than most - in the past, earthquakes are short and sometimes sharp. But this morning's lasted a lot longer than normal, the Herald's Jason Walls said.

Fire and Emergency NZ had not received any quake-related calls. A police spokesperson said no reports of major damage had been received, but officers are making enquiries around the lower North Island to assess any damage to property.

Wellington councillor Fleur Fitzsimons was on the phone to mayor Andy Foster - coincidentally talking about earthquake strengthening - when the quake hit.

"We were talking about quake strengthening to do with the Wellington central library - we're deciding this week - when I said: 'Andy! I think there's an earthquake'!"

"He said: 'I can't feel it, I'm driving'."

Fitzsimons described the event as "quite full on".

"They're usually short and sharp. But this was a long rattle. It lasted a decent 20 seconds. The doors were shaking and the kids were yelling out: 'What's that noise?'"

Fitzsimons acknowledged the coincidence, saying: "It definitely helped bring a sharp focus to the cause."

Wellington councillors are due to meet on Wednesday to discuss what its next move will be in relation to the Wellington central library, which has been closed since last year due to concerns it may not be able to handle a major earthquake.

There have been ongoing discussions about whether earthquake strengthening measures should be taken on the building - built in 1991 - or if it should be demolished altogether and rebuilt.

Horowhenua Mayor Bernie Wanden said council staff and emergency services were looking around Levin and the wider district for any signs of damage.

"So far, none to report of any significance, and in most situations it's been business as usual already which is great to hear."

Kāpiti Mayor K Gurunathan says there have been no initial reports of damage in the Kāpiti Coast but they have started checking facilities.

He's also relieved to hear Levin's had no reports of significant damage, and hopes it stays that way. He says it serves as a timely reminder there are other hazards to be aware about, other than the pandemic.

Horowhenua Chronicle editor Janine Baalbergen lives on the railway line in northeast Levin and said the quake sounded like a very heavy goods train going by.

"Everything shook and rattled but nothing fell over. Just a few crooked pictures on the wall, and elderly dog awoken but not fussed," she said.

Whanganui District Council Mayor Hamish McDouall said the 5.8 magnitude quake was pretty sudden and came in strong and hard.

"It was a very jittery quake and it got a bit stronger but I was very impressed the kids automatically went under the breakfast table."

He said it was the strongest earthquake he has felt since the Kaikōura earthquake in 2016.

McDouall said he had heard of no reports of damage so far in the Whanganui district.

"It's a good reminder that we live on fairly seismic active land and we just have to make sure we have enough water for three or four days and the things that can fall over are tied back."

Newstalk ZB's Scarlett Cvitanovich said it was felt in Whanganui and shook for around 30 seconds.

"This was the first significant earthquake I've felt since Christchurch and its many aftershocks. It arrived with a loud rumble in Whanganui and shook the house steadily for around 30 seconds," Cvitanovich said.

"It was long and rolling with a few sudden lurches but didn't lose its intensity."

Cvitanovich said she stood in the doorway with her parents as photographs started moving, some falling to the ground.

"You could hear house alarms starting straight away and sirens around the town."

Manawatū Guardian editor Merania Karauria, also in Whanganui, said it was "my first strong earthquake which seemed to go on forever. I am in an upstairs apartment and the shaking was scary. My cat ran to my bedroom. Being upstairs I was unsure where to stand. Items moved and I've moved bigger pieces onto the floor."

The Herald's Belinda Feek said it could be felt in New Plymouth quite strongly.

She said it was still shaking slightly after about 30 seconds.

Rangitīkei mayor Andy Watson said he hadn't received any reports of damage "as yet" due to the 5.8 magnitude earthquake.

"They will come in though, it was enough of a roll to cause some damage.

"Let's wait and see.

"When it struck, I thought 'uh oh, I hope this isn't Christchurch', because that would have been huge."

Ceramic wall hangings fell during the earthquake in Kapiti. Photo / Rosalie Willis
Ceramic wall hangings fell during the earthquake in Kapiti. Photo / Rosalie Willis

In Kāpiti, the quake was felt strongly. Rosalie Willis said "pictures fell off my walls" and said the shaking lasted about 10 seconds - with "a rumbling" continuing for a lot longer.

Kāpiti News editor David Haxton, his wife and two kids quickly gathered together in the middle of their Raumati Beach house as the shaking gripped the house.

"The cat bolted, thankfully there was no damage or worse, but it certainly raised the heart rate of everyone," he said.

Manager of The Mothered Goose in Bulls, Jaimee Simpson, said usually they do not feel earthquakes inside the cafe but as she was putting muffins in the oven she got a huge fright.

"I'm absolutely petrified of them and I was in here on my own so I had a bit of a meltdown."

She said there was no damage to the cafe and they are now all safe.

The owner of a beach-side Four Square in a town closest to this morning's 5.8 magnitude earthquake said the shake was nothing compared with the Christchurch earthquake.

Frank Tylor, who has owned the popular Waitarere Beach Four Square for more than 20 years, was in a unique position to judge earthquakes, having been on holiday in Christchurch when the big one hit in 2011.

He still remembers stepping outside to see a big concrete wave during the Christchurch earthquake, so the Levin quake was a little rattle in comparison.

"I lost a bottle of mayonaise off the shelf. That's about it," he said.

"It wasn't a problem."

Tylor said the earthquake struck as a group of more than 20 school children were waiting outside the convenience store for the school bus to take them to either college and primary school.

"They wait inside the shop when it's cold," he said.

As it was raining, all the schoolchildren were inside the store at the time. While there was no doubt there was an earthquake, he said they were all fairly subdued and just waited for the shaking to stop.

"No one was screaming, put it that way," he said.