The volcano, Mount Gamalama — which forms the entire island of Ternate in North Maluku province — erupted late Thursday and was still coughing up ash the following day.
While no one in the area has yet been told to evacuate, an airport in Ternate town at the mountain’s foot was forced to close, the transport ministry said.
“We closed the Sultan Baabulah airport this morning as the volcanic ash may pose a risk to planes,” said ministry spokesman J.A. Barata, adding that the airfield was covered with thick ash.
The airport could reopen Saturday if there are no further eruptions, Barata said.
Darno Lamane, an official at the volcano monitoring post, said the 1,715-metre volcano continued to spew ash in plumes of up to 600 metres on Friday.
A local disaster management agency official said that 11 hikers who had been at the volcano when it erupted managed to escape, but some were injured as they clambered down.
“There were 11 hikers injured while running down the slope during the eruption. Three of them are being hospitalised for broken bones,” Mansur Mahli said.
Indonesia sits on the Pacific “Ring of Fire” where continental plates collide, causing frequent seismic and volcanic activity. The archipelago nation is home to 129 active volcanoes, including 21 on Java.