Authorities recorded the volcano unleashing 10,000 metres (32,800 feet) of thick grey clouds.
Mount Lewotobi Laki-laki volcano in south-central Indonesia has erupted, spewing towering columns of hot ash into the air and prompting authorities to both raise the alert to the highest level and expand the danger zone to 8km (5 miles) from the crater.
The Indonesian Geological Agency said it recorded the volcano unleashing 10,000 metres (32,800 feet) of thick grey clouds on Tuesday afternoon.
The explosion of ash expanded into a mushroom-shaped cloud that could be seen from cities located 90km (56 miles) to 150km (93 miles) from the mountain.
There were no immediate reports of damage or casualties. Residents were warned to be vigilant about heavy rainfall triggering lava flows in rivers originating from the volcano.
