Residents near the 1,584 meter high top are urged to keep at least six kilometers away from the mountain and wear face masks. The head of Indonesia's geological agency also warns of possible lava flows in the area.
The preparedness has been raised to the highest level.
The eruption occurred during the night to Monday local time. It was followed by another a few hours later.
The volcano in the mountain, whose full name is Lewotobi Laki-Laki, has had several eruptions in the past year. Last autumn, nine people were killed in a massive eruption that forced several airlines to cancel departures to Bali.
