The increased incandescence of the crater glow, up from an intensity of one (faint) to three (bright), was attributed to fresh magma at the volcano’s mouth.
The bright crater glow was observed between 7:24 p.m. and 10 p.m. Thursday, and from 2 a.m. to 5 a.m. yesterday, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.
"At present, Mayon is in a mild stage of eruption as magma slowly intrudes toward the summit, subsequently pushing out recent hot lava," Phivolcs said in its latest bulletin.
Volcanologist Ed Laguerta, however, said the vicinity around Mayon still remains under alert level three since incandescent volcanic materials cascading down the volcano have not gone beyond the six-kilometer permanent danger zone.
Laguerta said Phivolcs will immediately raise Mayon’s alert level to four once the rate of magma intrusion increases.
During the period of intense crater glow, the number of rockfalls and magma-related tremors also increased. At least 48 high-frequency, short-duration harmonic tremors and one high-frequency and five low-frequency volcanic quakes were detected.
Meanwhile, Cedric Daep, chief of the Provincial Disaster Management Office, said vehicles are on standby around the perimeter of the six-kilometer permanent danger zone for quick evacuation of villagers if the situation worsens.
Daep said 17,155 people live inside the danger zone.  With Celso Amo and Felix de los Santos