New Zealanders have been warned not to go sightseeing in coastal areas and stay put on higher ground as a tsunami warning and beach and marine threat stays in place for many regions.

The alerts may stay in place until well into the afternoon, officials said today.

Emergency Management Minister Kiri Allan said it had been "an extraordinary morning for New Zealanders" around the country with many up from 2.30am worried about their homes and families.

This follows three major earthquakes in the Pacific region - one off the East Coast of New Zealand and two near the Kermadecs. The third of these earthquakes, a magnitude 8.1 shake, has triggered an almost New Zealand-wide tsunami activity alert, with a particular warning for parts of Northland, Bay of Plenty and East Coast.

For Aucklanders who are near beaches, there has not been any notification that they should be evacuated - but it has a beach and marine threat so they should stay off the beach and out of the water.

Those North Island residents who have had to "pick up their homes and evacuate" had done exceptionally well, said Allan.

They knew to head into the highlands when they felt a long or strong earthquake, she said.

The Government did not have timeframes for the evacuation. Allan warned it could be "quite lengthy" and even extend into this afternoon.

Allan said you don't ask people to evacuate lightly and so the assessments were done on who needed to leave their homes was done on a "risk to life" threat.

The entire town of Opotiki had been evacuated. Thousands of residents from other areas and towns had moved to higher ground.

She has been briefed by the national team in the bunker about the operations and called it a "dynamic event" that was constantly evolving.

Civil Defence in affected areas had been activated and were leading the responses on the ground, Allan said.

"People have done ... the right thing in the regions by picking up, packing up and by and large staying calm."

Those who have moved inland are being asked until there is the official all clear.

Allan said she knew people might get tired or bored but asked they not leave those areas.

National Emergency Management Agency controller Roger Ball said the severity of currents and surges would vary during the time that the warning was in effect for. "We ask that people don't go sightseeing - this is important."

Ball said the first waves could be smaller.

He asked that people stay 2m away from others if they are asked to evacuate.

GNS Science seismologist Bill Fry said there was no way to predict when the earthquakes would happen but they knew there could be more after the first one.

He said officials knew "time saves lives" so they aimed to respond quickly and get people evacuated.

Allan said it was completely natural to feel anxious but to try to stay calm, listen to messaging and to check on loved ones.

"It's absolutely natural in these times to feel high degrees of anxiety."