Police Deputy Commissioner John Tims confirmed that one person has died and "based on information we have, there are likely to be more".
Thirty-four people survived, with 31 still receiving treatment in hospital.
Prime Minister Jacinda Ardern, who travelled to the region, said the focus remained on the search-and-rescue mission and questions about whether tourists should be visiting would be addressed later.
"Soon as you're on the island, if there were to be a volcanic incident, it's going to be extremely hard to get immediate assistance", Cass said. I was basically just shocked.
Who was on the island?
23 people were taken off the island.
"This is a very, very hard day for a lot of Australian families whose loved ones have been caught up in this bad, awful tragedy", Morrison said. It said in a statement that the effects of the volcano can spread "many kilometres".
6 'probable' vaping-related lung injury cases linked to MA dispensaries
An diagnosis of about 1,800 of the hospitalized sufferers chanced on about 80% said they extinct on the least one THC product. Illicit vaping cartridge makers can choose the empty programs and then contain them with irrespective of they accumulate.
Of those, 13 people had been hospitalised and 11 were unaccounted for, he said.
Without providing details, Tims said police were launching a criminal investigation.
Ms Ardern acknowledged the apparently high number of Australian victims. "And how close we can get without it being very unsafe for our crew".
The website allows family members to register names of loved ones who have gone missing in a disaster.
What happened at the volcano?
The eruption began around 2.30pm, throwing a thick plume of white ash and smoke into the air.
Raymond Cas, an emeritus professor of geosciences at Monash University in Melbourne, Australia, told Radio New Zealand that he believed tourists shouldn't have been on the island. This number is expected to rise in the coming hours as police and rescue workers further investigate the scene.
But later private helicopter rescue missions picked up several people from the island.
Twelve people were killed on the island in 1914 when it was being mined for sulfur. He said one woman was badly injured but seemed "strong" by the end.