Three hikers – two Singaporeans and an Indonesian – have died in an eruption of Indonesia’s Mount Dukono volcano, where they found themselves in a no-go zone, officials said.

The eruption, on Halmahera island, sent an ash cloud about 6 miles (10km) into the air, with no towns of villages near enough to face any immediate threat.

Twenty hikers were on the slopes when disaster struck, the North Halmahera police chief, Erlichson Pasaribu, told reporters at a volcano monitoring station in Mamuya village. Nine were from Singapore and the rest Indonesian.

“To date, 15 climbers have safely descended,” Erlichson said several hours after the early-morning eruption.

The bodies of the dead hikers were still on the mountain, he said, without elaborating on the whereabouts of the remaining two. “Due to ongoing eruptions, the situation is still considered unsafe for evacuation. So, the joint team is still waiting for the right time to begin the search,” Erlichson said.

Some of the hikers had minor injuries and were taken to hospital for treatment. The group’s guide and a porter were taken to the police station and could face criminal charges for taking hikers into a prohibited area, said the police chief.

Since December, the national volcanology centre has been warning tourists and climbers not to come within two and half miles (4km) of the volcano’s Malupang Warirang crater after scientists spotted an increase in seismic activity.

Erlichson said the hikers had ignored social media appeals and warning signs put up at the entrance of the trail to stay away. “Local residents understand and don’t want to climb. Many [hikers] are foreign tourists who wish to create content,” he said.

Lana Saria, the head of the government geology agency, said Friday’s eruption was accompanied by a “booming sound” and a thick column of ash and smoke rising 10km from the summit of Mount Dukono. “The direction of the ash distribution leans northward, so residential areas and Tobelo city need to be vigilant for … volcanic ash rain,” she said.

It could be dangerous for public health, Lana said, and risked disrupting transportation services. There are no settlements within a radius of about five and half miles (9km) from the volcano.

Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity owing to its position on the Pacific “ring of fire”, where tectonic plates collide. The south-east Asian country has nearly 130 active volcanoes. Mount Dukono is currently on level 2 of Indonesia’s four-tiered alert system.

Erlichson urged hikers to stay away to avoid a repeat of Friday’s disaster, which had forced rescuers to deploy into in “tough terrain” even as the volcano continued rumbling. “After this incident, we will be strictly monitoring posts that hikers can pass. So no hiking as long as the status remains at level 2,” he said.