Sydney's Knox Grammar School has confirmed brothers Matthew and Berend Hollander have died in hospital from injuries sustained in Monday's White Island volcano eruption.

Key points: The fate of the boys' parents, Martin and Barbara Hollander, is still unknown

The fate of the boys' parents, Martin and Barbara Hollander, is still unknown Knox Grammar said the boys were "enthusiastic" and "well-liked"

Knox Grammar said the boys were "enthusiastic" and "well-liked" Seven Australians are confirmed to have died in Monday's White Island eruption

Matthew, who was in Year 8, and Berend, who was in Year 10, were holidaying in New Zealand with their parents Martin and Barbara, who remain unaccounted for.

The death toll from the disaster has now risen to eight, including seven Australians, but authorities have warned that is expected to rise.

The State Government says 10 adults from NSW who were injured in the disaster are being flown to Sydney to receive critical care.

Three arrived at Concord Hospital overnight, and one was taken to Royal North Shore Hospital.

In a statement, NSW Health said some of the 10 residents had "life threatening burn injuries".

In a statement, Knox Grammar headmaster Scott James said the brothers were enthusiastic, well-liked students.

"Matthew was involved in cadets and representing the school in basketball, squash and debating," he said.

"He was elected as a Mentor Representative in 2018/19. Matthew had a close circle of friends and was popular amongst his peers."

The boys' father, Martin Hollander, remains missing. ( Supplied: LinkedIn )

Berend, known as Ben, had a passion for baseball, AFL, cadets and software design.

"Ben's engaging smile and quirky sense of humour made him a good mate to his close group of friends and a welcome member to every classroom."

Mr James said it was a "devastating" loss for the community.

The boys' father, Martin Hollander, a former Knox student, is a Sydney investment director and freight initiatives manager for NSW Transport.

'Absolutely heartbroken'

The Hollander family released a statement saying they were "absolutely heartbroken by this loss".

"Ben and Matthew were wonderfully kind and spirited boys who lived short but very fulsome lives," it read.

"They loved Knox and all their friends, and the Australian sports and outdoor lifestyle they adopted on moving from the United States six years ago.

They had a positive and lasting impact on everyone's paths they crossed."

Friends of Jason Griffiths, Karla Mathews and Richard Elzer released a statement expressing sadness at Mr Griffiths' death. ( Supplied: DFAT )

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 was travelling on the cruise as part of a group of nine friends, all from Coffs Harbour, and two others in the group, Richard Elzer and Karla Matthews, remain unaccounted for.

Friends of the trio who did not make the ill-fated day trip to the island released a statement last night saying they were "incredibly saddened".

A total of 24 people on the island were passengers from the Ovation of the Seas cruise ship, which departed Sydney on December 4.