The Mount Sinabung volcano in Karo district has erupted intermittently since September, prompting authorities to raise the alert status to the second-highest level.
On Thursday it spewed hot ash 7,000 metres into the sky, said Sutopo Nugroho, a spokesman for the National Disaster Management Agency.
"The frequency of the eruptions has caused fear among the population and forced them to seek refuge in churches, mosques and other buildings away from the volcano," Nugroho said.
There have been no fatalities so far, he said.
Mount Sinabung had been dormant for 400 years before it erupted on August 2010.
There are nearly 130 active volcanoes across the Indonesian archipelago and eruptions are common.//DPA