Desperate efforts are underway to locate more than 20 people who are thought to be missing on New Zealand's White Island after a deadly volcanic eruption earlier on Monday.
Speaking at a news conference Monday, New Zealand National Operation Commander Deputy Commissioner John Tims said that there had been fewer than 50 people on the island at the time of the eruption.
So far 23 people have been evacuated, one of whom has died from their injuries. But an unknown number still remain behind on White Island, which police consider to be highly dangerous.
"At this stage it is too dangerous for police and rescue services to go on to the island ... the island is currently covered in ash and volcanic material," he said. There has been no communication from those remaining on the island since the eruption, he said.
Both New Zealanders and tourists have been caught up in the disaster, police said in a statement.
"Based on the information we have it is likely that there are other (fatalities)," the statement said. "Police are leading the search and rescue operation and we are working at pace to confirm the numbers of those involved."
Australian Prime Minister Scott Morrison confirmed on Twitter that Australians were involved in the volcanic eruption.
"Australians have been caught up in this terrible event and we are working to determine their wellbeing," he wrote.
More than 30 tourists from the nearby cruise ship Ovation of the Seas were on White Island at the time of the eruption, New Zealand Cruise Association chief executive officer Kevin O'Sullivan told CNN.
"Our hope is that everyone will be recovered quickly and unharmed," he said. The Ovation of The Seas is one of the largest cruise vessels in the world, according to operators Royal Caribbean.
Images of a crater on the island from cameras run by the Institute of Geological and Nuclear Sciences (GNS) appear to show a group of people inside the smoking center just minutes before the eruption.
Speaking at the news conference on Monday afternoon, GNS expert Ken Gledhill said that while the volcanic eruption hadn't been that large, it would have been hugely dangerous for anyone nearby.
"(The plume) went up 12,000 (feet) into the sky, and so on the scheme of things for volcanic eruptions, it's not large, but if you were close to that, it's not good," Gledhill said. The scientist added he couldn't predict whether there would be another eruption within 24 hours.
Prime Minister Jacinda Ardern said earlier that it was too early to say how bad the injuries were but added it was her understanding that a number of those affected were tourists.
Speaking to CNN-affiliate Radio New Zealand, St. John Ambulance said that up to 20 people are believed to have been injured in the eruption, adding that a mobile triage unit had been deployed.
Tourist Michael Schade and his family had been on the volcano just 20 minutes before it erupted. They were waiting on a boat, about to leave, when the eruption occurred.
Schade took videos of the ride leaving the island, showing giant plumes of thick black smoke as the boat quickly departed.
"Boat ride home ... was indescribable," Schade wrote on Twitter. "Those are some of the people (our) boat picked up. Praying for them and their recovery. Woman my mom tended to was in critical condition but seemed strong by the end."
Most active cone volcano
Photos from New Zealand's official geological hazard information site Geonet showed a huge plume of white smoke rising above the island on Monday afternoon, local time.
"Whakaari/White Island is erupting. More information soon," announced GeoNet in a notice on their official Twitter.
The White Island or Whakaari volcano is New Zealand's most active cone volcano according to the GeoNet website. It has been built up by more than 150,000 years of volcanic activity.
A cone volcano is the most immediately recognizable mountain-shaped variety, as opposed to shield volcanoes or calderas which are far more flat in shape.
A volcanic ash advisory was issued at 2:30 p.m. local time (8:30 p.m. ET Sunday) by MetService, New Zealand's meteorological service. New Zealand Police called for people in the affected ashfall areas to stay indoors.
The Volcanic Alert Level was raised to 4 shortly after the eruption, and the Aviation Color code is orange, according to GeoNet. Two hours later it was lowered to level 3, due to "diminished" activity in the area of the volcano.
New Zealand's National Emergency Management Agency said the eruption occurring at White Island is "hazardous in the immediate vicinity of the volcano" and that the agency is assessing the situation with scientific advisers to determine the severity of the threat.
Whakaari/White Island is dubbed "one of the world's most accessible active volcanoes" on a White Island Tours website, which offers ocean cruises near the island and a guided tour depending on the status of the varying volcanic alert levels.
According to the GeoNet website, more than 10,000 people visit the island every year.