Three hikers — two Singaporeans and a local — who were in an off-limits area died Friday in an eruption of Indonesia's Mount Dukono volcano, officials said. Several others were missing.

The eruption on Halmahera island sent an ash cloud about six into the air, but no towns or villages were close enough to face any immediate threat.

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

Nine were from Singapore and the rest were Indonesian, he said.

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

The bodies of the deceased were still on the mountain, he added, without elaborating on the whereabouts of the other two hikers.

"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 suffered minor injuries and were taken to a 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, the police chief added.

Indonesia is hit by frequent earthquakes and volcanic eruptions because it's on the "Ring of Fire," an arc of volcanoes and fault lines in the Pacific Basin.