Mount Soputan in North Sulawesi province, around 360 miles northeast of Palu, spewed ash 6,000 meters into the sky on Wednesday at 8.47am local time.
Officials raised the country's four-level volcano alert system from two to three, advising locals to stay away from the mountain and to have masks available in the event of ashfall.
Planes were warned of ash clouds because volcanic ash is hazardous for plane engines.
Soputan is on the northern part of Sulawesi island, where a central region was severely damaged by an earthquake and tsunami Friday. At least 1,234 died in the disaster, though the death toll is expected to rise sharply.
Indonesia has dozens of active volcanos.
The Independent
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