A volcano south-east of the Philippines capital spewed ash and steam about half a mile into the sky in a brief steam-driven explosion on Sunday, scattering ash in nearby villages and alarming residents, officials said.

The Philippine Institute of Volcanology and Seismology raised the alert level at Mount Bulusan in Sorsogon province following the 17-minute blast but added that there was no sign of an impending major eruption.

One of the country’s most active volcanoes, Bulusan has been showing signs of unrest with on-and-off ash and steam explosions in recent years.

“It is currently in an abnormal condition,” the government volcanology institute said, and asked people to stay away from a 2.4-mile (4km) permanent danger zone around the volcano.

Ash falls hit at least seven villages in and near the coastal town of Juban at the foot of Bulusan where people were asked to stay indoors and wear masks. Motorists were advised to drive cautiously on ash- and mud-covered roads.

Officials said they were assessing whether to evacuate residents, especially pregnant women, the elderly and children, from ash-hit villages.

Outside the permanent danger zone, the volcanology institute warned people, including those living on the vulnerable south-eastern side of the volcano, to stay alert “due to the increased possibilities of sudden and hazardous phreatic eruptions”.

Villagers living in valleys and along rivers and streams were warned to watch out for volcanic mudflows during the rainy season.

Aircraft were advised not fly close to the volcano in Sorsogon, which is about 373 miles (600km) south-east of Manila.

The Philippines archipelago, which has about two dozen active volcanoes, lies on the Pacific Ocean’s “Ring of Fire”, where volcanic activity and earthquakes are common.