Pictured: Rescue workers scour volcano during body recovery

New Zealand authorities have recovered six more bodies after a team landed on White Island to begin a high-risk operation to bring back victims of Monday's volcanic eruption.

The bodies are now on board the Royal New Zealand Navy's HMNZS Wellington.

The mission to recover two other bodies was eventually abandoned, however, with police saying there would be a "very limited" opportunity to look for them. Either people were killed in this week's eruption.

Authorities have faced growing pressure from families of the victims and the local community to bring back those killed as soon as possible.

New Zealand police had previously refused to go in due to safety risks, as experts warn the island remains highly volatile.

The country's geological science agency (GNS Science) said on Thursday that the risk of a further eruption over the next 24 hours was 50% to 60%.

Early on Friday morning, a blessing was held at sea with representatives of the families of those killed.

Just after first light, two helicopters from the New Zealand Defence Force left the township of Whakatane and began the 30m (50km) journey to the island off the country's eastern coast.

Scientists had warned gasses on the island are so toxic and corrosive that a single inhalation could be fatal.

Earlier, deputy commissioner Mike Clement said he expected the operation to take several hours and added that "the risk has not passed".

Specialist teams are due to arrive from Australia, Britain and the United States to treat the injured survivors in hospital burn units.

Dr Peter Watson, a chief medical officer, said during a previous news conference that extra skin had been ordered from US skin banks.

He said they estimated needing an extra 120 sq meters (1,300 sq feet) for grafting on to patients.

Authorities say 47 people from seven nationalities were visiting the island when it erupted - many were from a Royal Caribbean cruise ship that had left Sydney two days earlier.

There were 24 Australians, nine Americans, five New Zealanders, four Germans, two Britons, two Chinese and a Malaysian in the area at the time.

While no lawsuits have yet been filed, legal experts say they expect action in US courts by injured passengers and families of those who died.

Maritime lawyers claim the firm's potential liability could hinge on whether the eruption was an unforeseeable "act of God".

Royal Caribbean ticket terms posted on its website suggest the company is not liable for any injury, death or loss of property caused by an act of God - as well as war, terrorism or other events beyond the company's control.

It will likely argue the disaster was an extraordinary event no one could reasonably foresee, according to Robert Kritzman, a lawyer with Baker Donelson in Miami.

He said: "If a volcano were to erupt, clearly that isn't negligence on anyone's part, that's nature."

Royal Caribbean did not respond to questions about missing passengers or whether it told passengers of the risks of visiting the island.

In an email, the company said: "We grieve this tragic loss. We will to continue to offer our support and services to the families during this difficult time".

New Zealand Prime Minister Jacinda Ardern said on Thursday that some injured Australians had been medically evacuated and such flights would continue.

Australia previously said up to 10 such patients would be transferred to hospitals in Victoria and New South Wales states for further treatment.

White Island's volcanic alert has been lowered to two - there has been no further eruption since Monday, when the level had briefly been raised to four.

Its alert level since late Monday had been three, on a scale where five signifies a major eruption.