A volcano erupted in New Zealand on Monday, leaving five people dead and 50 more unaccounted for. Local police said tourists were seen walking inside the crater of White Island volcano moments before the deadly eruption.

Twenty-three people have been rescued, but it is unclear how many people remained on the island. Police say aerial reconnaissance flights have not identified any sign of life there, NZ News Hub reports.

White Island, also called Whakaari, is the country’s most active volcano.

Despite that, the privately owned island is a tourist destination with frequent day tours and scenic flights available as well as cruise ships that regularly drop by.

My god, White Island volcano in New Zealand erupted today for first time since 2001. My family and I had gotten off it 20 minutes before, were waiting at our boat about to leave when we saw it. Boat ride home tending to people our boat rescued was indescribable. #whiteisland pic.twitter.com/QJwWi12Tvt — Michael Schade (@sch) December 9, 2019

Police have said fewer than 50 people were on the island when the volcano erupted. Deputy Police Commissioner John Tims told reporters that “both New Zealand and overseas tourists” were believed to be involved.

The New Zealand Defence Force is now helping the rescue operation. A military plane has carried out surveillance and two helicopters and personnel are ready to assist.

Some of the missing were passengers from the Ovation of the Seas, a cruise ship owned by Royal Caribbean. It is currently at port in Tauranga, a coastal city near White Island.

Last photos: here are the White Island Tour operators rescuing people, timestamp 14:24 (~12-14 minutes after eruption). Endless gratitude to that crew for stepping up as first responders. I took these and reporters welcome to use with attribution. pic.twitter.com/ITmY1jCezr — Michael Schade (@sch) December 9, 2019

GeoNet describes White Island as New Zealand’s most active cone volcano.

The Bay of Plenty island is a popular tourist destination, with several holiday providers advertising guided tours of the inner crater.

Tourist Michael Schade posted footage of the eruption to Twitter (see above), saying he and his family had been at the crater shortly before the eruption.