The number of people identified as having died in the New Zealand volcano disaster has risen to eight, including six Australians.

Key points: Five Australians have been flown back for critical care

Five Australians have been flown back for critical care Two Sydney schoolboys are confirmed among those who died

Two Sydney schoolboys are confirmed among those who died Volcano experts say White Island remains "highly volatile"

Dozens of people are in various hospitals across New Zealand being treated for injuries on up to 90 per cent of their bodies.

Authorities are still unable to recover bodies from White Island following advice from experts that there is a 50 to 60 per cent chance of another eruption in the next 24 hours.

New Zealanders Hayden Marshall-Inman and Tipene Maangi have been confirmed among the dead.

Prime Minister Scott Morrison confirmed five injured Australians had been returned to Australia and were being treated in hospital, and another seven would be flown home in the next 24 hours.

The New South Wales Government issued a statement today saying four Australian adults were being treated in NSW hospitals.

NSW chief health officer Kerry Chant said some of the victims had life-threatening burns.

The Victorian Government confirmed that one person had arrived in the state this morning and was being transferred to the Alfred Hospital's burns unit.

Mr Morrison said in a statement that "any transfers will depend strictly on medical decisions from doctors that it is safe to move the patients".

The ABC has been able to confirm, via family and other associates, that at least six Australians died during or after the blast.

However, Mr Morrison has so far only confirmed one Australian fatality.

Late on Thursday morning, Mr Morrison gave the following details:

One Australian is confirmed dead

One Australian is confirmed dead 10 are missing, presumed dead

10 are missing, presumed dead Seven are expected to be evacuated home in next 24 hours

Seven are expected to be evacuated home in next 24 hours Five have already been flown to Australia

Five have already been flown to Australia One remains in a New Zealand hospital

Teen brothers among Australian victims

Brothers Berend and Matthew Hollander were travelling with their parents. ( Supplied )

On Thursday morning, Knox Grammar School in Sydney's north released a statement confirming the loss of two of its students — brothers Matthew Hollander (year 8) and Berend Hollander (year 10) — who died in hospital as a result of injuries sustained in the eruption.

The school said the boys' parents were still unaccounted for.

Among the other Australians confirmed dead are Brisbane woman Julie Richards, 47, her daughter Jessica Richards, 20, Adelaide man Gavin Dallow, and Jason Griffiths from Coffs Harbour.

Mr Griffiths, who died in hospital surrounded by loved ones, was travelling with eight other friends, including couple Karla Mathews and Richard Elzer, who are listed among those missing.

Several visitors were captured inside the crater just one minute before the volcano erupted on Monday. ( Supplied: White Island Crater Rim webcam )

The six friends released a statement through the Department of Foreign Affairs and Trade, saying they believed Ms Matthews and Mr Elzer also died in the tragedy.

"We discovered that two of our friends, Richard Elzer and Karla Mathews, were still on the island. We have been advised that there are no signs of life on the island," the statement read.

"We are incredibly saddened to have lost three of our closest friends."

It is now confirmed that 47 people were on or close to White Island when the volcano erupted: 24 Australians, nine Americans, five New Zealanders, four Germans, two Chinese, two people from the United Kingdom and one Malaysian.

Tricky recovery mission

All equipment on the island that monitors the volcano is still providing up-to-date information. ( Twitter: Michael Schade )

As hospitals continue to treat victims with severe burns, New Zealand authorities are working on how — and when — a recovery mission can be launched to retrieve the remaining bodies from the island.

Volcanologist Nico Fournier told a press conference on Thursday morning that all equipment on the island that monitors the volcano still works and is providing up-to-date information on volcanic activity.

He believes there is shallow magma that is driving activity under the surface and that "the level of tremor is increasing as we speak".

"The situation remains highly volatile. What we are trying to do to assist the operation is to provide an idea about the likelihood of another eruption over the next 24 hours," he said.

"To our best estimate, the likelihood of an eruption over the next 24 hours that would affect the area potentially where the rescue team would be is still between 40 and 60 per cent, so this is a high-risk operation."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 8 seconds 1 m 8 s Volcanologist Nico Fournier says there is a 40-60 per cent chance of eruption in the next 24 hours ( TVNZ )

Whakatane Mayor Judy Turner, who spoke at the same a press conference, said there was a growing sense of frustration and "desperation" among families wanting to bring their loved ones home.

"The frustration of those families most affected is completely understandable and the need for regular updates is now absolutely essential," she said.

"They are asking for messages to be confirmed to them what is being planned, who will be involved, how well they will be equipped, and how responsive those teams can be once clearance is given. That is a priority for them. No news is not good news for people in this situation."

New Zealand Police Deputy Commissioner Mike Clement said all those involved in the operation were "equally committed to finding a solution that safely gets us onto the island so that we can recover the people that we believe to be deceased on that island".

"That is the highest priority to us," he said.

Cr Turner said she was pleased a local with a high level of knowledge of White Island would be part of the recovery mission and they were expected to play an integral role in locating the bodies.

"This person knows exactly where the bodies are and so will be able to help the recovery team. This should mean that once they are on the island, their clear knowledge of where to look will save a lot of time and improve safety," she said.