About 20 climbers set out Thursday to ascend the nearly 1,355-meter (4,445-foot) volcano on the island of Halmahera, in defiance of safety restrictions, said North Halmahera police chief Erlichson Pasaribu.
They became stranded when Dukono erupted at 7:41 a.m. local time, spewing a thick ash column that rose about 10 kilometers (6.2 miles) above the summit. The eruption was recorded on seismographs for more than 16 minutes, Indonesia's Geological Agency said.
"They were aware that climbing was prohibited as the mountain is the restricted zone due to its high alert status, but insisted on going ahead," Pasaribu said in a television interview.
Rescue teams were deployed after receiving an emergency signal from the mountain area. Three men - two Singaporean and one Indonesian national - died at the scene, Pasaribu said.
As of Friday afternoon, 14 climbers including seven foreign nationals had been safely evacuated. Five of those evacuated were reported injured. Rescue teams continued to search for other climbers believed to be attempting to descend.
The bodies had not yet been recovered because continued eruptions and dangerous conditions prevented rescue teams from reaching the location.
The Center for Volcanology and Geological Hazard Mitigation has long banned activities within a 4kilometer (2.5mile) radius of Dukono's crater, citing hazards such as volcanic bombs, ashfall and toxic gases. Officials believe the hikers were inside the restricted zone at the time of the eruption.
Despite warnings on social media and signs at the site, "many people remain determined to climb, driven by the desire to create online content," Pasaribu said.
Mount Dukono is one of Indonesia's most active volcanoes and has been erupting almost continuously since 1933. Indonesia sits along the Pacific "Ring of Fire," an area of intense seismic and volcanic activity, and is home to more than 120 active volcanoes.
Authorities also warned of possible secondary hazards, including volcanic mudflows, especially during heavy rain, which could travel along rivers flowing from the volcano's slopes.
Volcanic activity at Dukono remains high, and authorities said it was at the second highest alert level. Authorities said the volcano has shown an increase in explosive magmatic eruptions since late March, with nearly 200 eruptions recorded since March 30 and an average of about 95 eruptions a day.
"Friday's eruption was among the strongest during this period," said Lana Saria, who heads Indonesia's Geology Agency at the Energy and Mineral Resources Ministry. She added that ash clouds ranging from white to gray and black in color were being blown northward.
She warned that ashfall could affect nearby settlements, including the town of Tobelo, raising health risks and disrupting transportation and daily life.
Officials urged residents, tourists and climbers to remain calm, follow official guidance and avoid restricted areas as monitoring of Mount Dukono continues.