The previously dormant volcano, more than 500 metres high, on the northern island of Kadovar off PNG erupted on Jan.5 with all 600 residents evacuated.
"It is hard today for us to collect data, especially ashes because of heavy rains", Daep said.
Mayon, although considered one of the country's most destructive volcanoes, is also one of its major attractions that continues to attract annually thousands of foreign and local tourists because of its description as "majestic" from its description as the "volcano with the world's most flawless cone". Traces of ash fell on Barangays Anoling, Sua, Quirangay, Tumpa, Ilawod and Salugan of Camalig and in Barangays Tandarora, Maninila and Travesia in Guinobatan.
"Phreatic eruption at Mayon Volcano at 8:49 a.m., ashfall should be expected on the southwest and west slopes", the Philippine Institute for Volcanology and Seismology (PHIVOLCS) said on its Facebook page on Sunday.
The Philippines has raised the alert level around an erupting volcano after signs magma is rising inside.
Phivolcs raised the alert to level 2, which means that the current activity is "probably of magmatic origin, which could lead to more phreatic eruptions or eventually to hazardous magmatic eruptions".
Mayon's biggest eruption was in 1841, when lava flows buried a town, killing 1,200 people.
Mayon, known for its near-perfect cone, last erupted in 2014.
PHIVOLCS further said the public should refrain from entering the 6-kilometer radius of the Permanent Danger Zone (PDZ) to minimize risks from sudden explosions, rockfall, and landslides.
Authorities advised people to cover their noses and mouths with a damp, clean cloth or dust mask if they were exposed to ash from the eruptions, and said aircraft must avoid flying close to the volcano's summit.
Experts say it has been displaying abnormal behaviour since late a year ago.
Romina Marasigan, the spokesperson of the Philippine National Disaster Risk Reduction and Management Council (NDRRMC), said on Sunday that 919 families have been so far subjected to "mandatory evacuation" by local officials due to the "abnormal activities" of the volcano.
Already, the authorities have ordered the evacuation of residents within the 6km radius permanent danger zone and a 7km extended danger zone on the southern flank due to the danger of rockfalls, landslides and sudden explosions or dome collapse that may generate hazardous volcanic flows.