Mount Sinabung has been erupting on and off since September, but went into overdrive late yesterday and early today, repeatedly spewing out red-hot ash and rocks up to eight kilometres (five miles) into the air.
Several thousand people left their homes overnight, taking the total number of those who have fled since the volcano rumbled to life to around 12,300, said the national disaster agency.
"People panicked last night as the eruption was accompanied by a loud thunderous sound and vibrations. Then it started raining down rocks," said local government official Robert Peranginangin.
He added there were no known casualties from the latest eruptions.
Also Read
The volcanology agency raised the alert level for the volcano, on the northern tip of Sumatra island, to the highest point on a four-stage scale, meaning a hazardous eruption is imminent or under way.
National disaster agency spokesman Sutopo Purwo Nugroho said the government was calling for people living within five kilometres (3.1 miles) of the volcano to leave their homes.
Sinabung, one of dozens of active volcanoes in Indonesia which straddles major tectonic fault lines known as the "Ring of Fire", erupted in September for the first time since 2010.
The country's most active volcano, Mount Merapi in central Java, killed more than 350 people in a series of violent eruptions in 2010.