Falling grit and ash accumulated up to 5 centimeters (2 inches) in already abandoned villages on the volcano's slopes, said Armen Putra, an official at the Sinabung monitoring post on Sumatra Island.
Farther afield in Berastagi, a tourist destination city in North Sumatra province, about 20 kilometers (12.4 miles) from the crater, motorists switched on headlights in daylight to see through the ash.
Videos and photos on social media showed people wore masks while outdoors.
There were no fatalities or injuries from the eruption, Indonesia’s Volcanology and Geological Hazard Mitigation Center said.
Villagers are advised to stay 5 kilometers (3.1 miles) from the crater’s mouth and should be aware of the peril of lava, the agency said. Air travel was not being impacted so far by the ash, the Transport Ministry said.
Some 30,000 people have been forced to leave homes around Sinabung in the past few years.
The volcano, one of two currently erupting in Indonesia, was dormant for four centuries before exploding in 2010, killing two people. Another eruption in 2014 killed 16 people, while seven died in a 2016 eruption.
Sinabung is among more than 120 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.