Seismic instruments detected several tremors as massive boulders tumbled to the ground, said Julio Sabit, of the Philippine Institute of Volcanology and Seismology.
But Sabit said that, while magma is still apparently rising, scientists will not likely raise the current "alert level three," of a maximum five, in the coming days.
He said the glow of magma from the crater was visible to the naked eye from the base of the 2,474-meter volcano.
The institute has maintained a level three alert since late January when increased seismic activity indicated possible eruption.
Volcanologist Ed Laguerta said the institute will raise the alert level to four once a sudden change in the ejection of magma is observed.
Mayon last erupted in February last year, driving 68,000 people from their homes.  Cet Dematera, Felix de los Santos