Mount Dukono on Indonesia’s eastern Halmahera island erupts on Friday morning, prompting an ongoing rescue and evacuation effort for hikers in the area, local officials say. Authorities report that three people have died, including two foreigners (reported as Singaporeans in several outlets) and one Indonesian resident. Additional hikers are missing, with figures across reports ranging from 10 missing to 20 missing; one outlet notes 20 were reported missing, including nine from Singapore.

The eruption produces a smoke and ash cloud rising roughly 10 km into the air, and is described by Indonesia’s geology officials as accompanied by a booming sound. The Indonesian disaster management agency says several climbers are injured. Search teams from regional disaster management and the national search and rescue agency continue sweeps and evacuations, but access is difficult because of rough terrain and ongoing volcanic rumbling that slows transport.

Mount Dukono is under heightened alert status on Indonesia’s four-tier warning system, and authorities say climbers had been warned not to enter nearby areas after increased volcanic activity. Some reports say the hike route was declared off-limits and that warnings and signage were in place before the eruption.