People from a district in Minahasa look at columns of ash spewed from Mount Soputan, in Indonesia's North Sulawesi province June 6, 2008.

Indonesia has raised the alert level for a volcano on Sulawesi island to the highest after it began spewing hot lava and clouds of smoke, a vulcanology official said on Saturday.

Lava from Mount Soputan has been gliding down its slopes about 1.5 km (0.9 miles) from the crater since Friday but has not reached the foot of the mountain, said Saut Simatupang, head of Indonesia's Vulcanology Survey.

"We have urged people to avoid areas near the volcano, especially camping areas in the eastern part of the mountain," he said, adding that residential areas near the volcano were not in any danger.

Indonesia has the highest number of active volcanoes in any country, sitting on a belt of intense volcanic and seismic activity known as the "Pacific Ring of Fire".

People often live and farm on the slopes of volcanoes because of the rich volcanic soil.

In the past two years, at least three major volcanoes, including Anak Krakatau, have showed signs of increased activity, but there has been no serious eruption.