What you need to know:
- Police said some 50 people were visiting White Island when it exploded in the early afternoon.
- Some 23 people made it off the island, five of whom have since died, the rest were being treated for injuries, including severe burns.
- Deputy commissioner John Tims said volcanic activity made rescue attempts by land too dangerous.
New Zealand police have said no more survivors were expected to be rescued from an island volcano that erupted suddenly on Monday, suggesting as many as two dozen people could have died.
Police said some 50 people were visiting White Island when it exploded in the early afternoon -- hurling ash and rock high into the air.
Some 23 people made it off the island, five of whom have since died, the rest were being treated for injuries, including severe burns.
It was earlier estimated the number still on the island was in double digits.
Police said early Tuesday that despite several aerial reconnaissance flights to try and find those trapped "no signs of life have been seen at any point."
"Based on the information we have, we do not believe there are any survivors on the island. Police is working urgently to confirm the exact number of those who have died."
As night fell, deputy commissioner John Tims said volcanic activity made rescue attempts by land too dangerous.
"I've got to consider the safety of our people and emergency services staff," he said.
The New Zealand military is expected to make a pass of the island at first light in the hope that people may have survived against the odds.
The eruption occurred just after 2pm (4am EAT), thrusting a thick plume of white ash 3.6 kilometres into the sky.
Seconds before, live camera feeds showed a group of more than a half dozen people walking on the crater floor. Then the images went black.
A "considerable number" of those caught up in the disaster are believed to be Australian, according to officials in Canberra.
As many as 30 of those involved are also believed to be cruise passengers on a day trip from the vessel Ovation of the Seas, Kevin O'Sullivan, chief executive officer of industry body the New Zealand Cruise Association told AFP.
The ship's operator Royal Caribbean -- who had billed the trip to White Island as "an unforgettable guided tour of New Zealand's most active volcano" -- said "a number of our guests were touring the island" but did not confirm that number.
The ship has a capacity of around 4,000 people and set sail from Sydney last week on a 12 day voyage.
Tourist Michael Schade, made it off the island just in time and was able to capture footage of the devastation.
His videos showed groups of startled tourists clustered by the shoreline, waiting to be evacuated as the ground around them smouldered, the sky filled with white debris. An ash-caked helicopter lay damaged nearby.
Volcanic Air said they had landed a helicopter on the island shortly before the eruption carrying four visitors and one pilot. All were now accounted for.
"It had landed on the island. What happened after that we don't know, but we know that all five made it back to Whakatane on one of the tourist boats," a company spokesman told AFP.
Guillaume Calmelet, the co-director of Skydive Tauranga, saw the eruption from above as he took a customer on a tandem skydive from a plane 12,000 feet above the Bay of Plenty.
"As soon as the parachute opened there was this huge cloud that was really different from whatever we've seen before," he told AFP.
"I could see it coming out in freefall, so probably about 30 seconds for the whole cloud to form, if that. It was pretty quick."
The country's National Emergency Management Agency described the eruption as "moderate", although the plume of ash was clearly visible from the mainland and from satellites flying overhead.
White Island -- - also known as Whakaari -- is about 50 kilometres offshore in the picturesque Bay of Plenty and is popular with adventurous tourists willing to don hard hats and gas masks.
It is New Zealand's most active volcano cone and about 70 percent of it is underwater, according to government-backed agency GeoNet.
Around 10,000 people visit the volcano every year. It has erupted frequently over the last half-century, most recently in 2016.
In August of that year the New Zealand Defence Force airlifted a 2.4-tonne shipping container onto the island to serve as an emergency shelter in case of an eruption.