There were no immediate reports of casualties after Mount Lokon, in northern Sulawesi province, belched Thursday night and again Friday morning, CNN reported.
The country's disaster management agency said it dispatched teams to assess the damage.
Indonesia's transportation officials warned airplanes to avoid routes near the volcano, a senior official told Xinhua, China's state-run news agency.
Volcanic smoke shot up to 2,000 feet into the air. Ash also pushed skyward.
"We have issued a warning for planes passing the area not to pass the routes near the volcano for their safety," Director General for Air Transport Herry Bhakti Gumay said.
The eruption so far hasn't affected national or international routes and airports in northern Sulawesi were operational, Bhakti said. Officials were monitoring air quality around the airports because volcanic activity remained high, he said.
"Airports have been informed to be alert," he said.