WHAKATANE, NEW ZEALAND (AFP) - The smouldering New Zealand volcano that killed at least six people is still too dangerous for emergency teams to recover bodies from, police said Wednesday (Dec 11), warning that many tourists who escaped the island were so badly burned they were not yet out of danger.

The official death toll after Monday's explosion on White Island climbed to six late Tuesday when another victim died in hospital.

The bodies of eight more people are believed to be on the island, but it is still too dangerous for the teams of rescuers to travel there and for forensic pathologists, odontologists and other victim identification experts to begin their work.

The Ministry of Health said 22 survivors still being treated in hospital burns units around the country remained in a critical condition.

When the volcano exploded it is believed to have sent superheated steam, ash and cannonball-like rocks hurtling from the caldera at supersonic speed.

Police Minister Stuart Nash said injuries to tourists and guides exploring at the time were so severe that some victims could not identify themselves.

"There are a number of people in hospital who cannot communicate, they have significant burns not only to skin but internal organs," he told Radio New Zealand. "We're working very closely with a number of agencies to ensure we get this identification right."

A total of 47 day-trippers were on the island when the blast occurred, hailing from Australia, the United States, Britain, China, Germany, Malaysia and New Zealand.

Mr Nash said the survivors were receiving world-class treatment but warned "there are still some very, very seriously injured people in hospital".

"We wish them the best but we're not out of the woods yet, of that there's no doubt," he said.

Australia says 13 of its citizens were being treated and 11 were unaccounted for, while two Britons have also been confirmed as injured and a local tour company says two of its guides are missing.

Malaysia's High Commission on Wednesday confirmed one of its nationals was critically injured, in addition to one previously announced death.

A coronial process has begun to identify the six confirmed dead but New Zealand police assistant commissioner Bruce Bird said their names and nationalities would not be released until the end of a formal process, which "can take some time".

Police have said they understand the frustration of family members who want clarity over the fate of their missing loved ones but recovery teams had no choice but to wait before accessing the island.

Seismologists have predicted there is a 50 per cent chance of another eruption on the island, which sits semi-submerged 50km out to sea.

Poisonous gases are still pouring from the volcanic vent and the island is blanketed in a thick layer of acidic ash.

"It would be madness for us to send men and women across to White Island in a situation that was not safe for them," said Mr Nash.

"We have a responsibility to New Zealand police staff to ensure any situation we put them in is safe."

New Zealand authorities said reconnaissance flights had determined soon after survivors fled the initial blast that there was no one alive on the island.

Police hope to deploy drones to measure toxic gas levels in the island's atmosphere and determine whether it is safe to return, but windy conditions have so far prevented them from being flown.

With weather expected to deteriorate on Thursday, pressure is building to start the recovery operation.

"We're assessing all factors every two or three hours to see if we can go," superintendent Bruce Bird told reporters.

The eruption at White Island - also known as Whakaari - occurred on Monday afternoon, spewing a thick plume of white ash 3.6km (12,000 feet) into the sky.

Visitors to the island, which is marketed as an adventurous day trip, included a group of more than 30 from a Royal Caribbean cruise ship, the Ovation of the Seas, which left Sydney on a 12-day voyage last week.

The ship had delayed its departure from nearby Tauranga in the wake of the disaster but set off for Wellington early on Wednesday morning.

"A team will remain on-site in Tauranga and all hospital locations to ensure those affected by Monday's incident are taken care of in terms of medical help, counselling, accommodations, and transport," the company said in a statement.

"Our priority continues to be to ensure that all guests and crew impacted are well taken care of."

The island in the picturesque Bay of Plenty attracts more than 17,000 visitors every year and is marketed as an experience for the adventurous traveller.

But the volcano's threat level had been raised in recent days, leading to questions about whether tour groups should have been allowed to visit.