Mount Rinjani on Lombok Island blasted ash and debris 3,500 meters (11,480 feet) into the air on Wednesday, said Sutopo Purwo Nugroho, the National Disaster Mitigation Agency spokesman.
The eruption shut down flights at the Ngurah Rai international airport in Bali, about 135 kilometers (84 miles) from Lombok, and the Selaparang airport in Mataram, the capital of West Nusatenggara province, located on Lombok Island, The Associated Press reported on Wednesday.
Airlines were told to avoid routes near the mountain and a decision about reopening the two airports would be made early Thursday, said Transportation Ministry spokesman Julius Barata.
The airport closures affected thousands of travelers, including those flying on Australian carriers Jetstar and Virgin Australia.
At Bali's airport, many travelers complained about a lack of information about their delayed flights and some were sleeping on benches inside terminals.
Farms and trees around the 3,726-meter (12,224-feet) -high volcano were covered in thick gray ash, but nearby towns and villages were not in danger, Nugroho said.
Rinjani is among about 130 active volcanoes in Indonesia. The archipelago is prone to volcanic eruptions and earthquakes because of its location on the Pacific "Ring of Fire," a series of fault lines stretching from the Western Hemisphere through Japan and Southeast Asia.