Mount Ruang, a stratovolcano in North Sulawesi Province, first erupted at 9:45 pm on Tuesday (1345 GMT) and twice again in the early hours of Wednesday, the country's volcanology and geological agencies said.

There were no reports of any deaths or injuries but more than 800 people were evacuated from two villages on Ruang island to the nearby island of Tagulandang, state news agency Antara reported.

The first eruption pushed an ash column two kilometres (1.2 miles) into the sky, with the second eruption pushing it to 2.5 kilometres, Muhammad Wafid, head of the geological agency said in a statement.

The volcanology agency said Tuesday that volcanic activity had increased at Ruang after two earthquakes in recent weeks.

The alert level for the volcano, which has a peak of 725 metres above sea level, was then raised from two to three, the second-highest possible level, before the eruption.

Authorities had also imposed a four-kilometre exclusion zone around the crater, which is more than 100 kilometres (62 miles) north of provincial capital Manado.

Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire", an arc where tectonic plates collide that stretches from Japan through Southeast Asia and across the Pacific basin.