Another person has died following a volcanic eruption in New Zealand, taking the death toll to six.
White Island, off the country's North Island in the Bay of Plenty, erupted with a large plume of ash and jets of scalding steam on Monday while dozens of people explored New Zealand’s most active volcano.
Authorities fear as many as 13 people may have been killed, while there are fears another eruption could be imminent.
Families now face an agonising wait to find out the fate of their loved ones.
Ronnie, aunt of a missing 23-year-old tour guide Tipene Maangi, said: "We were a bit shocked.
"We were shocked because up until then we didn't know what was really happening on the island. And we're still hopeful that he's still alive there somewhere."
New Zealand Police Deputy Commissioner John Tims announced the investigation as to why tour groups were allowed into the volcano zone despite scientists’ warnings of increased activity.
Investigators suggested there may be a criminal investigation into the matter, but later rowed back, suggesting it was too early.
Sarah Stewart-Black, the Civil Defence Emergency Management Director, said there was a "50 per cent chance" of another eruption of a similar or smaller size within the next 24 hours.
Ministry of Health spokesperson Pete Watson said 25 of the 31 injured were being treated at the nation's four regional burns units.
He added the burns units handled a typical year's workload in just one day. Most of the injured had burns covering more than 30 per cent of their body.
Conditions on the island remained too dangerous for rescue workers to attend on Tuesday, but officials said flyovers had revealed no signs of life.
Prime Minister Jacinda Ardern told parliament the “scale of this tragedy is devastating”.
“We know, too, there will be bigger questions in relation to this event. These questions must be asked and they must be answered,” she said.
“But our focus now is on discharging our duty of care to support those affected and that is also the focus of the police.”
The UK High Commissioner to New Zealand, Laura Clarke, confirmed two of the 31 people still in hospital were from Britain. It was not clear if more British tourists had been affected.
“We are supporting the family of two British women who have been hospitalised in New Zealand,” Ms Clarke tweeted.
It is believed most of the 47 people on the island at the time of the eruption were from Australia.
Australian Prime Minister Scott Morrison said 11 Australians were unaccounted for, with 13 in hospital. Three Australians were suspected to be among the initial five confirmed dead, he told reporters in Sydney.
Ms Ardern said New Zealanders and tourists from the United States, China, Britain and Malaysia were also affected.
The injured had been admitted to eight hospitals in the area, health officials said.
Media reports said plastic surgeons had been called in from several private practices to help hospitals treat the many people severely burnt in the eruption.
Westpac Rescue Helicopter Chief Pilot Roger Hortop compared the eruption to scenes straight out of a TV programme.
He said: "Everything was just blanketed in ash.
"There was a helicopter on the island that had obviously been there at the time with its rotor blades off.
"It's quite a shocking experience I suppose but we have to try and put that aside for now and get on with what we're doing."
White Island, also known by the indigenous Maori name Whakaari, is the tip of an undersea volcano 30 miles off the coast. Scientists had noted an increase in volcanic activity in recent weeks, leading to questions as to why tourists were still allowed on the island.
New Zealand’s GeoNet seismic monitoring agency had raised the volcano’s alert level on November 18 from one to two on a scale where five represents a major eruption. The advice noted an increase in sulphur dioxide gas, which originates from magma deep in the volcano.
GeoNet also said volcanic tremors had increased in strength from weak to moderate. It boosted the alert level to four after the eruption but lowered it to three on Tuesday as activity subsided.
Brad Scott, a volcanologist with research group GNS Science, said the alert level on White Island was often raised and dropped without an eruption. He said there had not been any major problems with tourists visiting the island in the past, though there had been some close calls.
“In the scheme of things, for volcanic eruptions, it is not large,” said Ken Gledhill from GeoNet. “But if you were close to that, it is not good.”
Richard Arculus, an Australian National University volcanologist who has made numerous visits to the island, said in addition to blasting rock and ash vertically, the eruption probably sent ground-hugging lateral blasts from the crater to the jetty, to which most tourists would have been returning as the activity increased.
“In that crater, it would have been a terrible place to be,” Mr Arculus said. “There would have been nowhere safe for you to be hiding, thinking that: ‘Oh well, if it explodes, it just goes straight up in the air.’”
New Zealander Geoff Hopkins, 50, was on the tour boat which had taken most of those affected to the island. Having returned to the boat early, he watched and helped the victims who were brought back.
“I don’t think there was anyone that came off who wasn’t badly burnt,” he told the New Zealand Herald.
Mr Hopkins said tourists in another group, which had used a helicopter, were relatively unscathed.
“Everyone else was horrifically burnt,” he said. “People were in shorts and T-shirts so there was a lot of exposed skin that was massively burnt. Their faces were massively burnt.
“But there were also huge burns under people’s clothes. So their clothes looked fine, but when you cut them off … I’ve never seen blisters like that.”
British Prime Minister Boris Johnson tweeted: “Devastating scenes in New Zealand. I’ve been in contact with Prime Minister @jacindaardern to express our deepest sympathies. There are many people still feared missing, and my heart goes out to all those affected and their families.”