Mount Soputan, located on the northern part of Sulawesi island, erupted twice on Sunday morning, said the country's national disaster agency.
Locals have been urged to wear masks in case of ash rain and to stay clear of the mountain in anticipation of hot ash and lava sliding down its slopes.
Authorities have also warned against the possibility of flowing of lava into rivers around the volcano.
The volcano's alert level is being kept at the second-highest level.
Soputan, which stands 1,784m tall, is one of more than 120 active volcanoes in Indonesia.
Its eruption came hours before a 6.2 magnitude earthquake struck more than 1,200 miles away in eastern Indonesia. The two are not likely to be linked.
The earthquake struck about about 101 miles southwest of the town of Jayapura, in the province Papua, according to the US Geological Survey.
Indonesia, an archipelago of more than 260 million people, is prone to earthquakes and volcanic eruptions due to its location on the Pacific Ring of Fire.
Additional reporting by agencies
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