The Philippines has raised the alert level at its rumbling Mayon volcano to "level 3" after detecting lava flow and indications of activity that could lead to eruptions of magma.
More than 900 families have been evacuated from villages near Mayon, a tourist attraction on central Luzon island, because of its near-perfect cone shape, following a "steam-driven eruption" on Saturday.
Authorities advised people to cover their noses and mouths with a damp, clean cloth or dust mask if they were exposed to ash from the eruptions, and said aircraft must avoid flying close to the volcano's summit.
Two similar "phreatic" eruptions occurred at the volcano in central Albay province on Sunday, unleashing more ash.
"Mayon's summit crater is now exhibiting bright crater glow that signifies the growth of a new lava dome and beginnings of lava flow towards the southern slopes," the Philippine Institute of Volcanology and Seismology (Phivolcs) said.
Phivolcs chief Renato Solidum said the volcano appeared due for another major eruption as it has been displaying abnormal behaviour since late last year.
"Alert level 3 is what we considered critical, 4 is when eruption is imminent, and 5 is eruption in progress," Cedric Daep, head of the Albay Provincial Disaster Risk Reduction and Management Office, said in a radio interview.
Mayon's most destructive eruption was in February 1841, when lava buried a town and killed 1200 people. It last erupted in 2014, spewing lava and forcing thousands of people to evacuate the area.
Since Saturday's first eruption, Phivolcs said it had recorded 158 rockfall events and urged people to stay away from a six-kilometre radius Permanent Danger Zone and a 7km Expanded Danger Zone on the volcano's southern flank.