This morning's powerful 5.8 magnitude earthquake was felt by a record 37,000 people, yet caused minimal damage, which scientists say is likely due to the depth and offshore positioning.

The earthquake struck at 7.53am, about 30km northwest of Levin at a depth of 37km.

It lasted about 30 seconds, causing many to duck for cover with the "long and rolling" tremors, and felt as far north as Auckland and near the bottom of the South Island.

Prime Minister Jacinda Ardern was live on television when it struck.

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

GNS Science seismologist John Ristau said although for many it was a "sharp jolt", the lack of damage was likely due to the depth and fact it was about 30km offshore.

"It was quite deep, so that mitigates a lot of the damaging effects, and being 30km offshore also helps a great deal. Then at 5.8 it is not so huge, and that all helps not cause any serious damage."

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The devastating Christchurch earthquake in 2011 was 6.3 magnitude, but at a depth of just 5km, and 10km south-east of the CBD.

The position offshore also meant it was in an area less-studied by scientists, and not linked to any known, major fault lines, Ristau said.

"It possibly occurred where the Pacific plate is subducting, being pushed under, the Australian plate, which is what happens in the North Island, but we are not exactly sure.

"It is not too surprising it occurred there though, as the Kāpiti Coast is quite an active area. There are often magnitude 3s and 4s, and we did have a 5.4 in the area looking back about 10 years.

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"We can safely say though that it is not linked to any major fault lines nor major earthquakes experienced in the past."

Due to the relatively small size of the quake there had been no tsunami risk, and also a low chance of it triggering any larger earthquakes, although smaller aftershocks were expected.

"We can't predict earthquakes and while there is a small chance it could trigger something larger, the far-more-likely scenario is that this will be the largest we'll see, with some smaller aftershocks."

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

One of the most interesting things was how many people reported feeling it - more than 37,000, a record, Ristau said.

"I think it was reported so widely because of its central location, close to Wellington and th top of the South Island, and the fact it was at a time of day when everybody is awake."

Deeper earthquakes also tended to be felt at a lesser degree more widely, while shallow ones more intense over a smaller area.

Almost 100 people reported it felt "severe" while 10 said it felt "extreme".