New Zealand Prime Minister Jacinda Ardern says aerial reconnaissance flights have found no signs of life on White Island after its volcano erupted, leaving eight people presumed dead.
And a New Zealand emeritus professor has described the tragedy as a disaster waiting to happen.
The volcano's two explosions in quick succession spewed a plume of ash thousands of metres into the air.
Five people are confirmed dead with eight others still missing. Some 31 people are in hospital and three have been discharged. Many of the injured were in critical condition, most from burns, Ms.Ardern said. Police said they did not expect to find any more survivors.
"To those who have lost or are missing family and friends, we share in your unfathomable grief in this moment at time and in your sorrow," Ms.Ardern said at a news conference in Whakatane, a town near the tourist attraction.
New Zealanders and tourists from Australia, the United States, Britain, China and Malaysia were among the missing and injured, she said, without giving more details.
Australian Prime Minister Scott Morrison said on Tuesday three Australians were feared to be among the confirmed fatalities, with 13 among the injured.
"I fear there is worse news to come," Mr Morrison said.
White Island is about 50 km from the east coast of North Island and huge plumes of smoke were visible from the mainland. Volcanologists said the ash plume shot 3,658 metres into the air.
Authorities were still assessing how close rescuers can get to the island.
"Ash is obviously significant," Ms Ardern said. "We've heard reports of one boat returning with up to half a metre of ash, so the ashfall is significant and that will be having an impact."
Ray Cas, a professor emeritus at Monash University, claims the island "has been a disaster waiting to happen for many years".
"Having visited it twice, I have always felt that it was too dangerous to allow the daily tour groups that visit the uninhabited island volcano by boat and helicopter," Cas said in comments published by the Australian Science Media Centre.
GeoNet raised the alert level for the White Island volcano in November because of an increase in volcanic activity.
The daily tours bring more than 10,000 visitors to the volcano every year. Passengers from a 16-deck cruise liner, Ovation of the Seas, were there at the time.
A crater rim camera owned and operated by GeoNet showed groups of people walking towards and away from the rim inside the crater, from which white vapour constantly billows, in the hour leading up to the eruption.
Ms Ardern praised helicopters who flew to rescue survivors immediately after the eruption.
"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," she said.
Australian Associated Press