Ash covered roads, vegetation and homes in the aftermath of the eruption, but no casualties were initially reported.

A volcano in the eastern Philippines spewed a huge, dark cloud on Sunday, prompting evacuations from ash-covered towns while authorities warned of possible further eruptions.

The blast from Bulusan volcano in the rural Sorsogon province lasted about 17 minutes, sending a grey plume shooting up at least one kilometre (0.6 miles), according to the Philippine Institute of Volcanology and Seismology (PhiVolcs).

No casualties were reported, but authorities raised the alert level to one on the five-level system, indicating "low-level unrest".

"There was a phreatic eruption of the Bulusan volcano, meaning the explosion was caused by the boiling water under the crater," PhiVolcs head Renato Solidum told local radio DZBB.

A group of 14 hikers and four local guides were midway down the 1,565-metre tall mountain, unaware that an ash cloud was shooting up on the other side of the mountain, civil defence official Leo Ferreras of nearby Barcelona town told AFP by phone.

"All of them got down safe and sound," he added.

The local government of Sorsogon, about 500 kilometres (310 miles) south of the capital Manila, said 10 villages in two towns were affected by the ashfall.

Images of the aftermath showed houses, roads, and trees in Juban town covered in ash, with vehicles struggling to navigate the road due to poor visibility.

Authorities deployed a fire truck to clear the area and residents helped sweep the ash off the roads.

"The evacuation is ongoing there, but our priority is senior citizens and those with asthma," Juban disaster official Dennis Despabiladeras said.

The Manila airport authority said no flights have been affected by the eruption so far, though pilots were warned about coming near the area.

Authorities reminded residents that entry into the four-kilometre radius around the volcano is prohibited and advised those living next to it to be cautious "due to the increased possibilities of sudden and hazardous phreatic eruptions".

Residents near the valleys and rivers were also alerted about the danger of mud and stream flows in the event of heavy rainfall.

Bulusan volcano has been active in recent years, with a dozen similar eruptions recorded in 2016 and 2017.

The Philippines is located in the seismically active Pacific "Ring of Fire" and has over 20 active volcanoes.