Doctors have revealed some of the horrific injuries suffered by tourists who survived the deadly volcano blast in New Zealand.

A total of 30 victims remain in hospital, with some suffering burns to as much as 95 per cent of their bodies.

Medical bosses at Middlemore Hospital, Auckland, as well as three other hospitals, have been operating on patients around the clock to save the injured.

Nick and Marion London from Engadine in southern Sydney are also in hospital with severe burns. (Supplied)

Middlemore Hospital's Chief Medical Officer, Dr Peter Watson said the type of burns suffered are complex.

"The nature of the burns suffered is complicated by the gases and chemicals in the eruption," he said.

"This has necessitated more rapid surgical treatment of these burns than is the usual case for thermal only burns.

Middlemore Hospital's Chief Medical Officer, Dr Peter Watson said the type of burns suffered are complex. (Nine)

"There a couple with less severe but the majority are very severe.

"Our surgical teams have been working around the clock."

An incredible 1.2 million square centimetres of skin grafts, as well as more dressings, have been urgently ordered from the USA.

An image provided by tourist Michael Schade shows White Island (Whakaari) volcano as it erupts. (Twitter/Michael Schade)

Most have 40-50 per cent burns, but others have suffered more.

"We're hoping that they will survive. We're doing the best to ensure that," Dr Vanessa Thornton, Clinical Director Emergency Department, said.

Dr John Kenealy, Clinical Director of Surgery and Perioperative Services at the National Burns Unit, said the number of patients they're dealing with at the same time is unprecedented.

Dr John Kenealy, Clinical Director of Surgery and Perioperative Services at the National Burns Unit, said the number of patients they're dealing with at the same time is unprecedented.Middlemore Hospital's Chief Medical Officer, Dr Peter Watson said the type of burns suffered are complex. (Nine)

He said 26 of the 31 patients had burns more than 30 percent of their body.

A total of 22 patients are on airway support due to the severity of their injuries, in what doctors said was an "unprecedented" situation.

One patient is due to be flown home by air ambulance from Auckland tonight to Australia, leaving 27 patients remaining in burns units across four hospitals.

So far six victims have been confirmed dead.

Jason Griffiths died in hospital after being treated for severe burns. (Supplied)

Dr Kenealy explained how burns victims are classified.

"The severity of a burn is primarily measured by how much of your body has been burned," he said.

"The skin's the largest organ in the body. It's approximately 20sq m in size. We measure in percentages.

"To give you an idea, the palm of the hand is about one and a half percent of the body.

Julie and Jessica Richards from Brisbane are confirmed to have died. (Supplied)

"So somebody whose got 30 percent of their body has got 30 of their palms burned.

"Some of the patients had 90 to 95 per cent. That means that three or four of their hands are not burned."

The defence force is preparing to bring others home when they are able to travel over the next few days.

A plane which can provide intensive care support will be used.

Surgeons at Middlemore Hospital have spent 500 hours in the operating theatre, with surgery for each patient lasting around eight hours.

As many as three operating theatres have been running, in what has been described as a year's worth of work for burns unit doctors in just one day.

Dr Watson said all patients have now been identified.

"The major issue was they didn't have any ID on them, and also the severity of their burns, many were in theatre," he said.