0916 GMT January 19, 2018
The 2,462-meter high volcano, a tourist attraction in central Albay Province because of its near-perfect cone shape, spewed ash and burning mud and rocks over the past two days, forcing more than 3,000 residents to evacuate from nearby villages, Reuters reported.
It showed a bright crater glow, signifying lava had started to flow from the crater.
Manila's airport authorities said airline Cebu Pacific had cancelled flights to nearby Legazpi City for a second day on Monday, citing bad weather.
Mayon's most destructive eruption was in February 1841, when lava buried a town and killed 1,200 people. It last erupted in 2014, spewing lava and forcing thousands of people to evacuate.
Renato Solidum, chief of the Philippine Institute of Volcanology and Seismology (Phivolcs), described Mayon's current activity as a non-explosive magmatic eruption, but he would not rule out a more dangerous volcanic explosion in coming days.
"What we would like to see is if there would be enough pressure, gas pressure for the next magma that would go up," he told ABS-CBN News Channel.
Phivolcs raised the volcano alert to level three late on Sunday after detecting the lava flow.
Solidum said raising the alert to level four, under which the danger zone would be expanded and a hazardous eruption could happen within a few days, depended on how Mayon behaved in the next few hours.
Level 5 indicates an eruption is in progress.
People have been advised to stay away from a 6km radius Permanent Danger Zone and a 7km Expanded Danger Zone on the volcano's southern flank.