It also ordered aircraft to give the volcano a wide berth.
Phivolcs also advised residents in nearby towns to avoid inhaling volcanic ash by covering their noses with wet towels and shutting windows.
But just within 24 hours of raising Alert Level 2 over Mayon, Phivolcs announced around 9 p.m. Sunday that the volcano was already placed under Alert Level 3.
In a separate incident, six people have been killed in central and southern Philippines due to landslides triggered by heavy rains over the weekend, local officials said.
Early Sunday, Philvocs raised the alert status of the area around Mayon to level two, "meaning the current unrest is probably of magmatic origin, which could lead to more phreatic eruptions or eventually to hazardous magmatic eruptions".
"Since the eruption, rockfall events have been intermittently recorded" while a "faint crater glow" was detected late Saturday night. Located in this areas are the villages of Anoling, Quirangay, Sua, Tumpa, Tinubran Camalig; Tandarora, Maninila, all in the municipality of Guinobatan; Miisi, Budiao, Banadero, Matnog of the municipality of Daraga; barangays Calbayog and Canaway, Malilipot; Buang Buhian and Magapo of Tabaco City; Baligang and Amtic in Ligao City.
Since Saturday's first eruption, Phivolcs said it had recorded 158 rockfall events and urged people to stay away from a 6km radius Permanent Danger Zone and a 7km Expanded Danger Zone on the volcano's southern flank.
South Africa vs India, 2nd Test, Day 2
Induces Kagiso Rabada to play a pull and Hardik Pandya does the rest at deep square leg by taking a forward-running catch. Shami achieved the milestone in his 29th Test, one more than the trio of Bishan Singh Bedi, Dilip Doshi and Pathan.
Mayon's most destructive eruption occurred in February, 1841 where lava flows buried a town leaving 1,200 people dead.
Under Alert Level 3, the extension of danger zone in the sector where the crater rim is low will be considered.
Phivolcs chief Renato Solidum said the volcano appeared due for another eruption as it has been displaying abnormal behaviour since late a year ago.
People living outside the danger zone but on the slopes of volcano were warned to take precautions against potential roof collapses due to the weight of ash and rainfall.
But Cedric Daep, head of the Albay Provincial Disaster Risk Reduction and Management Office, said those in evacuation centres may be allowed to return to their homes later in the day, unless the volcano alert level was raised further.
We have not reached the critical level, he said in a radio interview.