More than 12,000 people have been ordered to leave a 7km evacuation zone and there are warnings of destructive mudflows and toxic clouds.
“It is dangerous for families to stay in that radius and inhale ash,” Mr Claudio Yucot, head of the region’s office of civil defence, told AFP.
“Because of continuous rains in past weeks, debris deposited in the slopes of Mayon could lead to lahar flows (volcanic mudflows). If rain does not stop it could be hazardous.”
The volcano, a near-perfect cone, is about 330 kilometres southwest of Manila.
Steam-driven eruptions and rockfalls started over the weekend, and the crater began glowing on Sunday evening, in what the Philippine Institute of Volcanology and Seismology (Phivolcs) said was a sign of the growth of a new lava dome.
Lava last flowed out of Mayon in 2014, sending 63,000 people fleeing.
“We think the lava now is more fluid than in 2014. This means the flow can reach further down (the slopes) at a faster rate,” Phivolcs head Renato Solidum said. (tnp)