NZ volcano eruption survivors returned to Sydney, Melbourne as PM flags 'worse news'

All but one of the Australian survivors of the White Island volcano eruption are expected to be back on Australian soil in the next 24 hours, a number of whom have life-threatening injuries.

Seven Australians have already been airlifted to Sydney and Melbourne on four separate flights, New Zealand's Director General of Health Dr Ashley Bloomfield confirmed in a press conference this afternoon.

Another four flights are planned for later today, with most patients flying in to Sydney for treatment at specialist burns units at Concord and Royal North Shore hospitals.

One patient was taken to The Alfred Hospital in Melbourne this morning, while one more is expected to be transferred to an Adelaide hospital later today.

Of the six patients undergoing treatment in Sydney, two are critical, one is serious but stable and the condition of the other three are unknown.

Dr Bloomfield said the repatriation efforts were going "exceptionally well".

"The repatriation of remaining Australian patients will occur as their clinical state permits," he said.

"There is a very close liaison between our operations here and those in Australia at the receiving centres."

Dr Bloomfield said the repatriation efforts have required an "unprecedented" level of coordination between the two countries' health systems.

Of the 21 patients still in New Zealand, seven are Australian, two are New Zealanders and the remainder are a mix of other nationalities. Sixteen of them remain in a critical condition.

The patients are being treated at four different hospitals across the country.

"They continue to require the highest level of care and a small number are very unwell," Dr Bloomfield said.

"Our intensive care and burns teams throughout all of the burns unit continue to work around the clock putting in huge hours and showing, as we know they do, unbelievable commitment to ensuring the best of care to all patients."

Extensive supplies have also been sent from Australia, including 10,000 square centimetres of skin from the Australian Skin Bank to treat the patients' burns in the immediate aftermath.

But with an influx of serious burns patients coming into Australia, health authorities are now working to secure more donor skin to treat patients on home soil.

More than 1.2 million centimetres of donor skin is being sent to Australian and New Zealand from the United States, with the head of the Donor Tissue Bank of Victoria Dr Stefan Poniatowski saying there were simply not enough skin donors in Australia and New Zealand to cover this crisis.

Three Air Force planes – a C-130 Hercules from Richmond and two C-17 Globemasters from Amberley – have flown to Christchurch with specialist aircrew and medical equipment on board, in addition to aircraft supplied by the NSW, Queensland, Victorian and SA governments.

"Our hearts go out to all of the Australians and their families caught up in this tragedy, and our Kiwi cousins across the Tasman," Foreign Minister Marise Payne said in a statement.

"This is a time of immense grief and great sorrow for everyone involved."

"Our focus, and that of the New Zealand Government, is on providing the best, most immediate clinical care for those most in need."

A total of 47 people, including the Australians, were on the island when the blast happened.