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.
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.
Authorities have warned people off a six-kilometre radius around the volcano, and have restricted air travel in the vicinity.
Mayon in northeastern Albay province has erupted about 50 times in the last 500 years.
The biggest volcanic eruption in the Philippines was that of Mount Pinatubo in June 1991, which left around 850 people dead and affected over a million.
The Philippine archipelago is situated on the so-called Ring of Fire, an area of great seismic and volcanic activity around the Pacific Ocean, and has 23 active volcanoes.