New Zealand police has confirmed at least five people have been killed and more fatalities were likely, after an island volcano popular with tourists erupted Monday, leaving dozens stranded.

According to The Guardian, Deputy commissioner John Tims says that police and rescue have still not been able to access to island, after advice from volcano experts.

This means police are still unsure how many people remain on the island. “The physical environment is unsafe for us to return to the island,” he says

“A number of other people have been taken to hospital. A number of people have burns as a result of the eruption. It is still too early for police to confirm how many people are involved…including how many are still on the island.”

Prime Minister Jacinda Ardern confirmed some of those caught up in the disaster were foreigners. “We know that there were a number of tourists on or around the island at the time, both New Zealanders and visitors from overseas.”

New Zealand police also claimed that it was “too dangerous” to carry out volcanic rescues. Police said the eruption occurred about 2:11pm local time (0111 GMT) and there had been around 50 people nearby, fewer than the 100 officials originally estimated.

“Some of those people have been transported to shore, however a number believed to be on the island are currently unaccounted for,” the force said in a statement.

“Of those transported to shore, at least one has been critically injured.” St John Ambulance said there were up to 20 people believed injured but medical teams were still en route.

“Emergency services are currently frantically trying to get these people back from the island to hospital for treatment,” Whakatane mayor Judy Turner told news agency AFP.

There were particular fears for a group of visitors seen walking on the crater floor moments before the eruption occurred.

Cameras providing a live feed from the volcano showed more than half a dozen people inside the rim before images went dark when the eruption occurred minutes later.

The country’s National Emergency Management Agency described the eruption as “moderate”, although a thick plume of white ash could be seen for miles around.

Several helicopters and aircraft were seen in the area and survivors were pulled off the island in tour boats.

White Island is about 50 kilometres (30 miles) offshore in the picturesque Bay of Plenty and is popular with adventurous tourists willing to don hard hats and gas masks.

At least one group, four tourists and one pilot, who flew to the island on a Volcanic Air helicopter were accounted for, despite landing shortly before the eruption.

“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 news agency AFP.

White Island is New Zealand’s most active volcano cone and about 70 percent of it is under water, according to government 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.