The volcano, located on Ruang island about 100 km (62 miles) from the provincial capital Manado, has erupted more than three times since Tuesday.
Authorities have raised the alert level to the second highest level following the increased activity, Heruningtyas Desi Purnamasari, an official at Indonesia's Center for Volcanology and Geological Hazard Mitigation (PVMBG), told Reuters.
The eruption of Mt. Ruang were triggered by recent earthquakes on the island, with the mountain emitting dangerous and "explosive hot clouds" as high as 1.8 km (1.1 miles) into the sky, she said.
"We must clear the island because we anticipate there could be more eruptions. No activity is allowed within four kilometres from the crater," she said.
Footage seen by Reuters showed flows of red lava streaming down the mountain, reflected in the waters below, and billowing clouds of grey ash above its crater.
Ruang island is home to about 838 residents, most of whom have now been evacuated to the nearest island Tagulandang, said Heruningtyas.
Indonesia straddles the so-called "Pacific Ring of Fire," an area of high seismic activity that rests atop multiple tectonic plates.
