Authorities are closely monitoring Mount Sinabung on Sumatra, one of Indonesia's main islands, after placing in at the highest alert level last week.
Hot ash tumbled down Sinabung's slopes up to 2.5 kilometers (1.5 miles) from its smoldering mouth, government volcanologist Surono said.
He urged villagers to stay out of the main danger zone, which stretches 7 kilometers (4 miles) to the southeast of the crater. No injuries were reported.
"The growing size of the lava dome is very unstable," said Surono, who goes by one name, adding that smoldering rocks mixed in with hot gases may tumble down at any time.
More From This Section
Mount Sinabung is among about 130 active volcanoes in Indonesia, which is prone to seismic upheaval due to its location on the Pacific "Ring of Fire," an arc of volcanoes and fault lines encircling the Pacific Basin.
The 2,600-meter (8,530-feet) Mount Sinabung has sporadically erupted since 2010, after being dormant for 400 years. An eruption last year killed at least 17 people.