Areas around the crater of the volcano, located about 1,900 km (1,181 miles) northwest of the capital, Jakarta, have been off-limits for several years because of frequent volcanic activity.
The Bureau of Meteorology’s Volcanic Ash Advisory Centre (VACC), in Australia’s northern city of Darwin, issued maps on Monday showing an ash cloud heading in three directions from Sinabung, to the north, northwest and south-southeast.
Indonesia also upgraded its Volcano Observatory Notice for Aviation (VONA) to red, its highest warning, and said the ash-cloud top had reached 23,872 feet (7,276 meters), according to a ground observer.
Sinabung is about 75 km (47 miles) southwest of Kualanamu International Airport in Medan.
Nur Isnin Istianto, head of the regional airport authority, said Kutacane airport in Aceh province had been closed, but the wind direction allowed the airport of Kualanamu, Meulaboh and Silangit to remain open.
Sutopo Purwo Nugroho, a spokesman for Indonesia’s Disaster Agency, said the eruption began on Monday morning, accompanied by multiple earthquakes and showering surrounding villages with small rocks.
“In five districts it became dark with a visibility of about 5 metres,” he said in a statement.
No casualties were reported. The agency urged the public to stay out of a 7-km (4-mile) exclusion zone around the crater, and watch for further warnings, which could cover floods.
The 2,460-metre (8,071-ft) tall volcano is among Indonesia’s most active. When Sinabung erupted in 2014, more than a dozen people were killed and thousands were evacuated. Prior to recent times, its last known eruption was four centuries ago.
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