According to the Philippine Institute of Volcanology and Seismology (Phivolcs), the seismic network around Mayon Volcano recorded 19 low-frequency, one explosion-type and two high-frequency earthquakes in the past 24 hours.
Phivolcs said the "shallow movement of magma below the summit crater" is causing the low-frequency earthquakes.
Steam emission from the summit, however, has remained weak, it added.
The other day, a minor ash explosion occurred following 147 low-frequency earthquakes.
The ash column rose about 500 meters above the crater before drifting to the southwest.
A small explosion-type earthquake recorded by seismographs accompanied the ash ejection.
Because of the seismic unrest that may lead to hazardous and sudden steam-driven explosions, Phivolcs raised alert level 2 and advised the public to stay away from the six-kilometer radius permanent danger zone and avoid major river channels emanating from the volcano.