New Zealand police have said they do not believe they will find any more survivors after a devastating volcanic eruption engulfed tourists on the country's White Island, killing at least five.

Key points: Forty-seven people were on the island during the eruption

Forty-seven people were on the island during the eruption Five people are confirmed dead, eight are still missing and 31 are being treated in various hospitals

Five people are confirmed dead, eight are still missing and 31 are being treated in various hospitals Three people were released from hospital after being treated

At the time of the eruption, New Zealand police said 47 people were on the tiny island, off the east coast of the North Island.

It happened at 2:11pm local time, blasting plumes of white smoke, ash and debris 12,000 feet into the sky.

Twenty-three survivors were taken off the island by rescuers after the eruption, but five of those died.

Eight people remain unaccounted for and 31 patients are being treated in seven hospitals. Three were treated and released.

Rescue workers are still searching for the missing, but New Zealand Prime Minister Jacinda Ardern said they had to be careful as the area was dangerous.

An experienced tour guide is the first of the victims to be identified — Hayden Marshall-Inman from Whakatane in New Zealand was among those who died, his brother Mark confirmed on social media.

Mr Marshall-Inman was remembered as a "lovely young man" who died doing what he loved, and as "energetic" by former Whakatane mayor, Tony Bonne.

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Authorities said most of the evacuees had suffered burns.

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Ms Ardern said this morning that four helicopters were able to land on the island and save people.

"In the immediate aftermath, a number of helicopters made a deliberate decision to fly to the island to rescue survivors," Ms Ardern said.

"I want to acknowledge the courageous decision made by first responders and those pilots who, in the immediate rescue effort, made an incredibly brave decision under extraordinarily dangerous circumstances in an attempt to get people out."

New Zelanders as well as tourists from Australia, the US, Britain, China and Malaysia are among those missing and injured.

The New Zealand Red Cross has started a list for those worried about a loved one or who want to register themselves as alive.

Late on Monday, police said aircraft scouring the island for any signs of life had not seen any survivors.

"Police believe that anyone who could have been taken from the island alive was rescued at the time of the evacuation," a statement said.

"Police are working urgently to confirm the exact number of those who have died, further to the five confirmed deceased already."

Operation will involve air and sea searches

A New Zealand Defence Force ship is approaching the island and will deploy drones at first light.

Police have said the island is still too dangerous for anyone to land on it.

Australian Prime Minister Scott Morrison said a number of Australians had been caught up in the "terrible tragedy", including 24 Australians who were visiting the island as part of a cruise ship group.

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He said Australian authorities had so far only been able to identify the Australians who had been hospitalised and hoped to know more in the morning.

"We must prepare for some difficult news in the days ahead," he said.

Foreign Minister Marise Payne said consular authorities were moving to help Australians "hurt" in the eruption.

A woman on a boat takes a photo of the volcano on White Island just moments after it erupted. ( Twitter: Michael Schade )

The captain of the Ovation of the Seas cruise ship said some passengers and crew had been on the island at the time of the eruption and had not returned.

Police did not reveal the nationalities of the dead, but appealed for people who had friends or relatives on the island to get in touch.

'Devastation is an understatement'

The chairman of White Island Tours, Paul Quinn, said the company was "deeply saddened" by the disaster.

"Devastation is an understatement," he said.

White Island Tour operators land on White Island minutes after the volcanic eruption. ( Supplied: Michael Schade )

"This is a terrible tragedy and our thoughts and prayers are with everyone who has been impacted."

He said the company was assisting police and Civil Defence with the recovery effort.

"Our immediate focus is on supporting our staff, manuhiri [visitors] and respective whanau [extended family], who have been significantly impacted and are showing immense strength and courage," he said.

Another eruption can't be ruled out

Ms Ardern travelled to nearby Whakatāne soon after the eruption.

She would not be drawn on the question of whether tourists should have been allowed onto the island.

"The absolute focus needs to be the search and rescue," Ms Ardern said.

Just one minute before the eruption, webcam footage captured what appeared to be people walking inside the tiny island's volcano crater.

Ken Gledhill from the New Zealand geological agency GNS Science told a press conference the eruption was a "throat clearing" and said the volcano had "showed increased activity for the last few weeks".

"We can't be certain there won't be another eruption in the next 24 hours," he warned.

Geology expert Chris Elders said although the volcano had shown a recent increase in unrest, there was "very little warning" the eruption would take place.

Ovation of the Seas captain says passengers remain unaccounted for

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In an announcement made onboard the Ovation of the Seas, the captain said: "At the moment our priority is to ensure that every single one of our guests and crew is accounted for."

He said the ship was waiting for solid information from the New Zealand Government but confirmed there were passengers and staff on the island when the volcano erupted.

"We kindly ask that you keep the guests and crew and their families in your thoughts and prayers."

The ship was due to sail on Monday evening but will remain in the Port of Tauranga.

"We will remain in the Port of Tauranga as long as necessary," the captain said.

"We ask for your patience, understanding and support during this time.

"The safety of our guests and crew is always our top priority."

The Ovation of the Seas, which can carry nearly 5,000 people, left Sydney on December 4 and was due to return to Australia on December 16.

Minutes from disaster

Eyewitness Michael Schade tweeted dramatic video footage of the events and said the tour group he was with had been on the edge of the main crater just 30 minutes before the eruption.

Footage Mr Schade posted to Twitter showed smoke billowing from the island, with a mangled, ash-covered helicopter sitting by the shore.

White Island Tour operators take a boat load of survivors away from White Island. ( Supplied: Michael Schade )

"My god, White Island volcano in New Zealand erupted today for first time since 2001," Mr Schade tweeted.

"Our whole tour group were literally standing at the edge of the main crater not 30 minutes before."

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Mr Schade said that while he was lucky to have left the island, tour operators went back soon after to rescue people "12-14 minutes after the eruption".

He then described how his mother tended to an injured woman in the boat taking them off the island.

Smartraveller contact details: If you are concerned about the welfare or whereabouts of a loved one, contact Smartraveller. 1300 555 135 (within Australia)

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"My family and I had gotten off it 20 minutes before, were waiting at our boat about to leave when we saw it. Boat ride home tending to people our boat rescued was indescribable," he said.

"My thoughts with the families of those currently unaccounted for, the people recovering now, and especially the rescue workers.

"Praying for them and their recovery.

"Woman my mom tended to was in critical condition but seemed strong by the end.

"The helicopters on the island looked destroyed."

The New Zealand Herald posted a photo of a person covered in ash, laying on a stretcher.

Tourist attraction with a deadly past

GeoNet, New Zealand's geological hazard information centre, describes White Island, also known as Whakaari, as New Zealand's most active cone volcano.

A satellite image shows White Island before the eruption. ( Google Maps )

About 70 per cent of it is under the sea.

Twelve people were killed on the island in 1914 when it was being mined for sulphur. Part of a crater wall collapsed and a landslide destroyed the miners' village and the mine itself.

The remains of buildings from another mining enterprise in the 1920s are now a tourist attraction, according to GeoNet.

The island became a private scenic reserve in 1953, and daily tours allow more than 10,000 people to visit the volcano every year.

Geonet raised its alert level to four then later lowered it to three (from a maximum of five) and the country's aviation code has been raised to orange amid concerns about the impact on flights.

A volcanic ash advisory has also been issued for the surrounding area.