Five dead, tourists unaccounted for after White Island volcano erupts in New Zealand's Bay of Plenty

Video by Michael Schade

Australians are among dozens of people caught up in New Zealand's volcanic eruption, which has killed least five people.

Police expect the fatalities to grow after New Zealand's Whakaari, or White Island, volcano erupted on Monday afternoon.

As many as 27 people have been left stranded on New Zealand's most active cone volcano, with their condition unknown.

Police and emergency services haven't been able to reach or make contact with those trapped by the blast.

Australians are believed to be among the visitors from a nearby cruise ship, the Ovation of the Seas, which originated in Sydney, on Whakaari.

 Volcano erupting on New Zealand's White Island. Picture: Michael Schade via Twitter

Volcano erupting on New Zealand's White Island. Picture: Michael Schade via Twitter

"Australians have been caught up in this terrible event and we are working to determine their wellbeing," prime minister Scott Morrison tweeted.

"I have been in touch with (New Zealand prime minister Jacinda Ardern) to offer our full support with whatever they need and our authorities are working closely together."

The resultant ash plume has created conditions too dangerous for access.

Emergency will attempt to reach the island as soon as it is safe to do so.

Several people suffering from injuries, including burns, are being treated in nearby Whakatane Hospital and Middlemore Hospital.

They are among 23 people, of the police estimation of 50, to have made it away from the island in time.

Ms Ardern rushed to nearby Whakatane on Monday night, where grim expectations are held.

"I know there will be a huge amount of anxiety for those who have loved ones on or around the island at the time. I can assure them police are doing everything they can," Ardern said.

Ardern said those on the island were a mix of Kiwis and overseas visitors.

Royal Caribbean, owner of Ovation of the Seas, issued a statement saying the ship would stay in the nearby port of Tauranga overnight "until we learn more about the situation".

The island is frequently visited by tourists as part of organised boat tours from Whakatane.

Geological hazard trackers GeoNet had registered moderate volcanic unrest on the island for weeks.

But the nature of volcano activity is unpredictable, with the eruption unforeseen by authorities.

A GeoNet camera of the crater's rim, set to take pictures every 10 minutes, showed a string of people visiting the crater at 2:10pm.

The next shot taken, at 2:20pm, was unreadable as the blast had rendered the camera inoperable.

Earlier, St John has dispatched seven helicopters to the island, but they are unable to land.

"We are taking expert advice with regard to conditions to determine when we can safely access the island," a police statement read.

"We can confirm there has been one fatality, and based on the information we have it is likely there are others."

Police did not advise of any further information of the deceased person.

Aviation meteorologists have issued an "orange" volcanic ash advisory, which reflects the potential to affect nearby flights.

Police have also advised nearby residents to be aware of the potential for ashfall from the eruption.

By 3pm AEDT, GeoNet had reduced the alert level from four to three, noting a "steady decline in activity since the eruption".

Australian Associated Press