A powerful volcanic eruption has rocked New Zealand’s White Island, a small uninhabited volcanic islet sticking up out of the sea in the Bay of Plenty, 50 kilometres offshore of the country’s North Island.

The eruption took place with little warning Monday afternoon local time while dozens of tourists from cruise ship Ovation of the Seas were touring the volcano.

The New Zealand police force says that  50 people were present on the island when the eruption took the visitors by surprise. Several people have been reportedly injured, and some have been evacuated to the mainland. At least seven people are critically injured.

Five people have already been pronounced dead, and there are fears that the number could rise.

New Zealand is located in one of the world’s most tectonically-volatile regions. Vulcanologists say that while the eruption was relatively small compared to other past disasters, anyone close to the site would have been in serious danger.