Indonesia issued a red alert on Friday after Mount Karangetang on the island of Sulawesi erupted, sending lava and searing gas clouds down its slopes, a volcanologist said.
"We raised the volcano's status to the highest red alert level today at 5:45 pm (local time) and ordered an evacuation in three villages on the slopes," government volcanologist Surono said.
He said that the 1,784-metre mountain on the sparsely-populated island off North Sulawesi oozed lava, heat clouds and debris reaching as far as 3,800 metres away down its slopes.
"The eruption is still going on and its current activity remains high," he said.
"The main threat is heat clouds that will be fatal for people living in villages on the slope."
The volcano killed four people during an eruption in August 2010.
Indonesia sits on the Pacific "Ring of Fire" where continental plates collide, causing frequent seismic and volcanic activity. The archipelago nation is home to 129 active volcanoes, including 21 on Java.