A rescue mission was underway on Friday in eastern Indonesia as 20 hikers went missing following a volcanic eruption.

Three of the missing people, including two foreigners, are reported to have died.

What do we know?

Mount Dukono, located on the Halmahera island in North Maluku province, erupted on Friday ​at 07:41 a.m. local time (10:41 pm UTC Thursday), spouting volcanic ash up to 10 ​kilometers (6.2 miles) high into the air, Indonesia's volcanology agency said.

Twenty hikers, nine of them from Singapore, were reported missing shortly after.

"There are three dead, two foreigners and one resident of Ternate" island in east Indonesia, Erlichson Pasaribu, the police chief of North Halmahera, told Kompas TV.

Dozens of rescue personnel have been deployed to search for the trapped hikers, Iwan Ramdani, the head of the local rescue agency, ​told Reuters news agency.

Since April 17, the area has been officially off-limits for visitors after scientists observed an increase in volcanic activity.

Mount Dukono on third-highest alert

Government geology agency head Lana Saria said in a statement that Friday's eruption was accompanied by a "booming sound."

The agency maintained the alert status ‌at Mount Dukono at the third-highest level in the country's four-tiered volcano alert system, she said.

"The direction of the ash distribution leans northward, so residential areas and Tobelo City need to be vigilant for... volcanic ash rain," the agency head added.

Authorities also warned residents to steer clear of any activities within 4 ​km (2.5 miles) ⁠of the crater.

Indonesia straddles the Pacific Ring of Fire, a tectonic zone with intense seismic and volcanic activity.

Edited by: Wesley Rahn