Visitors are evacuated during the volcanic eruption at New Zealand's White Island, Dec. 9, 2019. (Photo provided by Michael Schade/Handout via Xinhua)

Three Australians are believed to be among those killed in New Zealand's volcanic explosion, Prime Minister Scott Morrison said in a press conference on Tuesday morning.

Morrison said 24 Australians aged between 17 and 72 were on a tour of White Island on Monday when the volcano erupted, and 13 of them are hospitalised across multiple hospitals in New Zealand, with 11 Australians still "unaccounted for."

"But with 11 Australians unaccounted for, three of those are feared to be amongst the five that have already been identified as deceased."

The first victim has been identified by the local media as Hayden Marshall-Inman, a local tour guide.

Photo taken on Dec. 9, 2019 shows the heavy smoke from volcanic eruption at New Zealand's White Island. (Photo provided by Michael Schade/Handout via Xinhua)

"This is a very, very hard day for a lot of Australian families whose loved ones have been caught up in this terrible, terrible tragedy," Morrison said.

"A time of great innocence and joy interrupted by the horror of that eruption," he said, expressing gratitude to the New Zealand government and the country's Prime Minister Jacinda Ardern.

"I want to thank all of those who risked their lives yesterday, put themselves in harm's way to protect others," he said.

"These horrible incidents are always accompanied by incredibly selfless acts. And equally I want to thank all of those in the medical teams who are there caring for Australians right now in New Zealand hospitals."