Nearly 15,000 people have left the mostly poor farming communities within a six-kilometre radius of Mayon's crater in northeastern Albay province in forced evacuations since volcanic activity spiked last week.
Albay's governor extended the danger zone by one kilometre on Monday and asked thousands of residents to be ready to move anytime.
But many opted to flee from the expanded danger zone even before the mandatory evacuation order.
After days of showing signs of renewed restiveness, including a swarm of rockfalls and a bright-orange crater glow visible at night, Mayon began expelling lava on Sunday night, which flowed slowly down two gulleys on its southeastern slope, government volcano experts said.
An ash plume that shot up to 100 metres at dawn on Tuesday drifted southeastward with the wind toward some villages, said Teresito Bacolcol, director of the Philippine Institute of Volcanology and Seismology.
An AP video showed a boulder getting ripped from the side of a dome of lava in Mayon's crater then plunging and breaking into smaller red-hot pieces as it rolled down and smashed onto other stones on the volcano's steep slope.
The 2462-metre Mayon is a top tourist draw in the Philippines because of its picturesque conical shape but is the most active of 24 known volcanoes in the archipelago.
It last erupted violently in 2018, displacing tens of thousands. In 1814, Mayon's eruption buried entire villages and left more than 1000 people dead.
The volcano had been raised to alert level three on a five-step warning system on Thursday, meaning a hazardous eruption is possible in weeks or days.
