Authorities have extended a danger zone around a rumbling volcano in western Indonesia after it spewed blistering gas farther than expected, forcing panicked residents to flee down the sides of the mountain.

Mount Sinabung's booming explosion just after midnight on Sunday triggered a panicked evacuation. Men with ash-covered faces streamed down the scorched slopes on motorcycles, followed by truckloads of women and children, many crying. Officials shouted instructions on megaphones as stones and debris rained from the sky.

More than 50 eruptions on Saturday sent lava and searing gas tumbling out of the volcano in the North Sumatra province down the south-eastern slopes up to three miles away, said Indonesia's disaster mitigation agency spokesman Sutopo Purwo Nugroho.

The volcano was still spitting clouds of gas and lava as high as 4,000 metres (13,000 ft) in several eruptions on Sunday, but no casualties were reported.

Nugroho said the danger zone south-east of the volcano was extended from 3 – 4 miles from the crater's smouldering mouth.

Soldiers joined the rescue operation in two villages of Jewara and Pintu Besi, about 4 miles from the crater, where homes and farms were caked in grey dust. More than 20,000 people have been evacuated from villages around the crater into several temporary shelters since authorities raised the alert status for Sinabung to the highest level in November.

"We were tired here ... we've lost everything. We wonder about our lives after this disaster," said Anton Sitepu, a father of four who is among those in a cramped shelter in the village of Telagah.

Mount Sinabung has sporadically erupted since September. An eruption in 2010 killed two people and caught scientists off-guard because the volcano had been quiet for four centuries. A transportation ministry spokesman said airlines were notified to avoid routes near the mountain.

Mount Sinabung is among about 130 active volcanoes in Indonesia, which is prone to seismic upheaval due to its location on the Pacific "ring of fire", an arc of volcanoes and fault lines encircling the Pacific basin.