Locals scrambled to escape after the Semeru volcano on the east of Java island began spewing out clouds of smoke and ash.
No casualties or damage to buildings have been reported, the Indonesian disaster agency (BNPB) said.
Videos show local residents running as a huge plume of towering smoke and ash blankets nearby villages in the East Java province.
Thoriqul Haq, a local official, told Reuters that a road and bridge connecting the area to the nearby city of Malang had been severed.
“This has been a very pressing, rapid condition since it erupted,” he said, adding that evacuations are underway.
A resident living in a nearby village posted a photo of the eruption on social media, writing; “Friends, please pray for me, I hope my family is fine, Just now, it’s really bursting.”
The 3,676-meter (12,060-foot) Semeru had last erupted in January, with no casualties. It is among Indonesia’s nearly 130 active volcanoes.
Indonesia, an archipelago of more than 270 million people, is prone to earthquakes and volcanic activity because it sits along the Pacific “Ring of Fire,” a horseshoe-shaped series of fault lines.
