Updated January 15, 2018 18:23:12

More than 9,000 people have evacuated the area around the Philippines' most active volcano as lava flows down its crater in a gentle eruption that scientists are warning could turn explosive.

The Philippine Institute of Volcanology and Seismology increased the alert level for Mount Mayon late on Sunday to three on a scale of five, indicating an increased tendency toward a hazardous eruption.

Residents from the Albay area on the island of Luzon have been evacuated.

Institute head Renato Solidum said lava flowed at least half-a-kilometre down a gully from the crater and on Monday morning, ash clouds appeared mid-slope.

Molten rocks and lava at Mayon's crater lit the night sky on Sunday despite thick clouds, sending thousands of residents into evacuation shelters.

Mayon in north-eastern Albay province has erupted about 50 times in the past 500 years.

Photo: A local photographer, Earl Recamunda, shared pictures of the volcano's glowing crater on Facebook. (Supplied: Earl Recamunda)

AP

Topics: volcanic-eruption, philippines, asia, pacific

First posted January 15, 2018 17:37:43