New Zealand police and military specialists have launched a risky operation to recover the bodies of eight victims of a volcanic eruption on an island that has left at least eight others dead.

Just after first light on Friday, two helicopters from the New Zealand Defence Force lifted off from the township of Whakatane and travelled 50 kilometres (30 miles) to White Island off New Zealand's eastern coast.

Eight military specialists wearing protective clothing and using breathing apparatuses landed and are trying to recover the bodies, police said. Scientists have warned that gases on the island after Monday's eruption are so toxic and corrosive that a single inhalation could be fatal.

Police Deputy Commissioner Mike Clement told reporters Thursday evening that drones had pinpointed six bodies but the location of two others was unknown. He expected the operation to take several hours.

Police, military and other personnel will monitor the recovery operation from a ship stationed just off the island. Volcanologists aboard will use electronic equipment on the island to provide the recovery team with real-time information on the volcano's behaviour.

New Zealand volcano: Eruption in photos Show all 20 1 /20 New Zealand volcano: Eruption in photos New Zealand volcano: Eruption in photos Smoke from the volcanic eruption of Whakaari, also known as White Island. New Zealand police said the blast had left five people dead, but that number will now rise to include those people who were still on the island when it erupted allessandrokauffmann via Reuters New Zealand volcano: Eruption in photos Emergency services attend to an injured person TVNZ via Reuters New Zealand volcano: Eruption in photos Thick smoke from the volcanic eruption SCH via Reuters New Zealand volcano: Eruption in photos The volcano on New Zealand's White Island spewing steam and ash moments after it erupted Michael Schade/AFP via Getty New Zealand volcano: Eruption in photos White Island Tour operators rescuing people minutes after the volcano erupted Michael Schade/AFP via Getty New Zealand volcano: Eruption in photos Thick smoke from the volcanic eruption from a distance of a vessel SCH via Reuters New Zealand volcano: Eruption in photos An aerial photo shows White Island after its volcanic eruption New Zealand Herald via AP New Zealand volcano: Eruption in photos An aerial view shows smoke bellowing above the crater of Whakaari GNS Science via Reuters New Zealand volcano: Eruption in photos Emergency services attend to an injured person arriving at the Whakatane Airfield New Zealand Herald via AP New Zealand volcano: Eruption in photos This handout photograph courtesy of Michael Schade shows the volcano on New Zealand's White Island spewing steam and ash minutes following an eruption on December 9, 2019. - New Zealand police said at least one person was killed and more fatalities were likely, after an island volcano popular with tourists erupted on December 9 leaving dozens stranded. (Photo by Handout / Michael Schade / AFP) / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / MICHAEL SCHADE" - NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS == NO ARCHIVE (Photo by HANDOUT/Michael Schade/AFP via Getty Images) HANDOUT Michael Schade/AFP via Getty New Zealand volcano: Eruption in photos A wreckage of a helicopter amid ash minutes after the volcano on New Zealand's White Island erupted Michael Schade/AFP via Getty New Zealand volcano: Eruption in photos SCH via Reuters SCH via Reuters New Zealand volcano: Eruption in photos This image released by GNS Science, shows plumes of smoke from a volcanic eruption on White Island, seen from Whakatane, New Zealand Monday, Dec. 9, 2019. A volcano erupted Monday on a small New Zealand island frequented by tourists, and a number of people were missing and injured after the eruption. (GNS Science via AP) GNS Science via AP New Zealand volcano: Eruption in photos An aerial view shows smoke bellowing above the crater of Whakaari, also known as White Island, volcano as it erupts in New Zealand, December 9, 2019, in this image obtained via social media. GNS Science via REUTERS ATTENTION EDITORS - THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. MANDATORY CREDIT. NO RESALES. NO ARCHIVES. WATERMARKS AT SOURCE. GNS SCIENCE GNS Science via Reuters New Zealand volcano: Eruption in photos epa08056782 A handout photo made available by the New Zealand Police shows White Island (Whakaari) volcano, as it erupts, in the Bay of Plenty, New Zealand, 09 December 2019. According to police, at least five people have died in the volcanic erruption at around 2:11 pm local time on 09 December. The island is located around 40km offshore of the Bay of Plenty. EPA/NEW ZEALAND POLICE HANDOUT BEST QUALITY AVAILABLE MANDATORY CREDIT HANDOUT EDITORIAL USE ONLY/NO SALES NEW ZEALAND POLICE HANDOUT EPA New Zealand volcano: Eruption in photos An aerial view shows hikers walking on the crater rim of Whakaari, also known as White Island, shortly before the volcano erupted GNS Science via Reuters New Zealand volcano: Eruption in photos Emergency services at Whakatane Airport Getty Images New Zealand volcano: Eruption in photos A rescue helicopter arrving at the airport Getty Images New Zealand volcano: Eruption in photos White Island (Whakaari) volcano, as it erupts Michael Schade/EPA New Zealand volcano: Eruption in photos White Island (Whakaari) volcano, shortly before erupting Michael Schade/EPA

Scientists have warned volcanic activity has increased in recent days and the island is "highly volatile."

That has delayed the recovery of the last victims since Monday's eruption, which occurred as 47 tourists and their guides were exploring the island. In addition to the bodies left on the island, eight other people were killed and dozens were severely burned by the blast of scalding steam and ash.

"The risk has not passed," Mr Clement said. "The people who are going to be protected by the equipment they will wear tomorrow are few and far between and so we have spent considerable time making sure we have the right people with the right skills and the right equipment."

Clement said the success of the operation would depend on many factors beyond the control of the recovery team, like "the mountain itself, the volcano, the weather and other matters, environmental factors that we don't control."

"A lot has to go right for this to work," he said.

"We will all be waiting tomorrow morning to ensure that the people who are putting themselves in harm's way in the interests of recovering those bodies, our thoughts and our prayers and our love will be with them."

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New Zealand medical staff were working around the clock to treat the injured survivors in hospital burn units, and specialist medical teams are due to arrive from Australia, Britain and the United States.

The enormity of the task was clear when Dr Peter Watson, a chief medical officer, said at a news conference that extra skin has been ordered from American skin banks. Hospital personnel anticipated needing an extra 120 square metres (1,300 square feet) of skin for grafting onto patients, Dr Watson said.

White Island is the tip of a mostly underwater volcano that is about 50 kilometres (30 miles) off New Zealand's North Island and has been a popular attraction visited by thousands of tourists each year.

Authorities say 24 Australians, nine Americans, five New Zealanders, four Germans, two Britons, two Chinese and a Malaysian were visiting the island Monday at the time of the eruption. Many were from a Royal Caribbean cruise ship that had left Sydney two days earlier.

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.

New Zealand's GeoNet seismic monitoring agency on Thursday lowered White Island's volcanic alert level to 2, noting there's been no further eruption since Monday, when the level had briefly been raised to 4. Its alert level since late Monday had been 3 on a scale where 5 signifies a major eruption.