The ash puffs occurred at 6:25 a.m., 2:58 p.m., 4:56 p.m. and 5:48 p.m. Monday, and 12:26 a.m. yesterday.
In a bulletin, Phivolcs said the grayish to dark brown ash clouds reached about 100 to 500 meters into the air and drifted west-northwest.
Lesty Saquillon, Phivolcs science research specialist, said the ash explosions were due to the continuous magma ascent building up pressure inside the volcano.
"The series of small explosions indicates that Mayon is exhibiting a slight increase in its level of activity," Phivolcs said, adding that more ash explosions are expected in the coming days.
Seismic sensors detected 313 tremors and 24 volcanic earthquakes. Mayon’s sulfur gas emission reached 3,364 tons last Monday.
Volcanologists said lava continued to flow toward the Miisi and Buyuan gullies.
Alert level 4 still remains hoisted around Mayon, which means that an explosive eruption is highly possible.