"Probable intrusion of magma at depth may or may not lead to a magmatic eruption", Phivolcs said. This is the second phreatic eruption of Mayon which was recorded following a similar phenomenon which lasted for nearly two hours on Saturday afternoon.
"Since the eruption, rockfall events have been intermittently recorded and are continuing as of the time of the release of this bulletin".
In the second eruption, the volcano emitted a grayish steam and ash cloud as sulfurous odor was also detected where rumbling sounds were heard by residents in Barangay Anolong in Camalig.
Phivolcs said: "For the past 24 hours, Mayon Volcano in Albay province has noticeably increased its unrest".
After three phreatic or steam-driven eruptions and 158 rockfall events between 4:21 p.m. on Saturday and 7:25 p.m. on Sunday, the institute said Mayon's summit crater "is now exhibiting bright crater glow that signifies the growth of a new lava dome and beginnings of lava flow towards the southern slopes".
In view thereof, DOST-PHIVOLCS is raising the Alert Level of Mayon Volcano from Alert Level 1 (abnormal) to Alert Level 2 (increasing unrest).
The agency advised local government units and the public to stay away from the four-kilometer radius Permanent Danger Zone. The institute advised people near ashfall to cover their noses and mouths with a damp, clean cloth or dust mask.
Mayon's biggest eruption was in 1841, when lava flows buried a town, killing 1,200 people.
The authorities have warned people off a six-km radius around the volcano, and have issued a level 2 alert as concern grew over the possibility of stronger and more unsafe eruptions.
Mayon, known for its near-perfect cone, last erupted in 2014.
We have not reached the critical level, he said in a radio interview.
Albay Public Safety and Emergency Management Office head Cedric Daep announced the barangays in the towns of Daraga, Camalig, Guinobatan, Malilipot, Tabaco City, and Ligao City.
Under Alert Level 3, the extension of danger zone in the sector where the crater rim is low will be considered.