JAKARTA - Indonesia's smouldering Mount Sinabung volcano yesterday spewed volcanic ash that blanketed parts of the city of Medan, located some 50km north-east of the mountain.

Residents in Medan in North Sumatra province were forced to cover their faces with masks after the volcanic ash was carried by winds blowing towards the city, said the local disaster mitigation agency head Subur Tambun, according to the Associated Press. Local television aired footage of the ash engulfing parts of the city.

Data from the monitoring post showed there were seven hot ash avalanches yesterday that surged up to 3,500m towards the south- east, while ash clouds swelled some 2,000m high.

The Volcanology and Geological Disaster Mitigation Centre has already set a danger zone of 3km radius from Mount Sinabung's peak, but on the south and south- eastern parts, the zone has been extended to a 7km radius from the summit. On the south-eastern and eastern sides, the danger zone is a 6km radius.

Ash from Mount Sinabung also reached Medan city last week.

Nearly 10,000 people have been evacuated since Sinabung began erupting violently two weeks ago, spewing hot ash and rocks into the air. The authorities raised the alert status for the volcano to the highest level at the start of this month, after detecting a sharp increase in activity. Sinabung came back to life two years ago after a period of inactivity, and 16 people were killed last year in a fierce eruption.

The volcano has had a devastating economic impact in the past. The disaster agency estimates that it caused more than US$100 million (S$134 million) in damage last year and in 2013 over a broad range of sectors, including infrastructure, farming and tourism.