INDONESIAN authorities ordered the evacuation of 15,000 residents near an active volcano in the west of the vast archipelago yesterday as they raised the alert for the emergency to the highest level.

Mount Sinabung on the island of Sumatra has become increasingly active in recent months, spewing columns of ash several kilometres into the air.

Authorities have expanded the evacuation radius to 5km (three miles) from 3km and the military geared up to help move residents out.

About 6000 people have already been evacuated from the area, which is 88km from Medan, capital of North Sumatra province.

No casualties were initially reported as the status of the volcano was raised from "standby" to "caution".

"We have raised the status to 'caution', which is the highest of level for volcanic activity because we anticipate there will be more eruptions and because the intensity of eruptions has been increasing," the National Disaster Mitigation Agency said in a statement.

Mount Sinabung is one of nearly 130 active volcanoes in the world's fourth-most populated country, which straddles the "Pacific Ring of Fire".

The most deadly eruption in recent years was of Mount Merapi in 2010, near the densely populated city of Yogyakarta in central Java. More than 350 people were killed.