New Zealand police do not expect to find any more survivors of a volcanic eruption on White Island that killed at least five people.
"No signs of life have been seen at any point," police said in a statement after rescue helicopters and other aircraft carried out a number of reconnaissance flights over the island following the eruption on Monday afternoon.
"Police believe that anyone who could have been taken from the island alive was rescued at the time of the evacuation," the statement added.
Australians are believed to be among the visitors on Whakaari from a nearby cruise ship, the Ovation of the Seas, which originated in Sydney.
Up to 50 people were on or near the island when the eruption took place.
As many as 27 people may have been left stranded, with their condition unknown.
"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 to have made it away from the island in time.
Ardern rushed to nearby Whakatane on Monday night, where expectations are grim.
"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 the cruise ship, 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.
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".