Indonesia says it will evacuate hundreds of people living near Mount Lokon on Sulawesi island after raising the volcano's alert status to the highest level.
"We raised the volcano's status to the highest red alert level last night. There was a significant rise in volcanic activity since July 9. The volcano spewed ash 500 metres into the air over the weekend," government volcanologist Kristianto told AFP.
"Today we will be evacuating people living within a 3.5-kilometre radius around the volcano as a precautionary measure, in case of a bigger eruption which may be accompanied by deadly searing gas," he added.
Around 28,000 people live within the evacuation zone but only "hundreds" will be moved Monday, those in the path of the ash, as officials continue to monitor volcanic activity, disaster management agency spokesman Sutopo Purwo Nugroho said.
Officials said tourists would also be barred from going on popular day hikes to the 1,580-metre Mount Lokon, one of the most active volcanoes in Indonesia and located 20 kilometres away from North Sulawesi provincial capital of Manado.
The volcano erupted in 1991, killing a Swiss tourist.
Mount Soputan, another volcano in North Sulawesi province, erupted early this month, spewing ash and smoke 5,000 metres into the air.
The Indonesian archipelago has dozens of active volcanoes and straddles major tectonic fault lines known as the "Ring of Fire" between the Pacific and Indian oceans.
The country's most active volcano, Mount Merapi in central Java, has killed more than 350 people in a series of violent eruptions which started in late October.