Prime Minister Scott Morrison has confirmed 24 Australians were among the five dead, eight missing and 31 rescued and hospitalised after a volcano erupted on White Island, off New Zealand's North Island.
Two tour groups comprising 47 people were on White Island or Whakaari on Monday afternoon but 39 people made it off, NZ Deputy Police Commissioner John Tims said on Tuesday.
Of the number, five died in hospital, three were discharged overnight and 31 are being treated, while eight are still missing and feared dead.
The groups included locals who were part of the tour operations, as well as Australians, Americans, British, Chinese and Malaysians.
Late on Monday evening, Mr Morrison tweeted that 24 Australians had been visiting White Island around the time the volcano erupted and they were among the people “who are unaccounted for”.
The Prime Minister said that he had been in touch with the New Zealand Prime Minister and the two countries were working to get more information.
“We hope to know more in the morning, however we must prepare for some difficult news on the days ahead,” Mr Morrison added.
Fly-overs by rescuers did not find any signs of life but authorities will not venture on to the island until it is safe to do so.
White Island erupted at 2.11pm local time (12.11pm AEDT) on Monday, sending a huge plume of ash more than 3600 metres into the air.
The Australians were believed to have been among the visitors from a nearby cruise ship, the Ovation of the Seas, which left Sydney last week sailing for Auckland.
NZ authorities made the grim announcement Monday evening that aerial reconnaissance flights over the island failed to find “any signs of life”.
“Police believe that anyone who could have been taken from the island alive was rescued at the time of the evacuation,” they said in a statement.
“Based on the information we have, we do not believe there are any survivors on the island.”
Earlier on Monday, New Zealand Police confirmed five people had died and warned more fatalities were expected.
Ms Ardern rushed to nearby Whakatane on Monday night, where expectations were 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.
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 nearby Whakatane.
Among those on the ship was Nigel Walker from Wollongong in Sydney’s south.
"It's tragic… I was only saying to my mother-in-law before the cruise that White Island would be a great pĺace to visit,” he told The New Zealand Herald.
Michael Schade, who is believed to be from San Francisco, wrote on Twitter he visited the crater 30 minutes before the eruption.
“My god,” he wrote on Twitter as he posted video of the eruption.
“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.
“This is so hard to believe.”
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 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".
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