Phivolcs has raised Alert Level 2 over the volcano, which means the "current unrest is probably of magmatic origin, which could lead to more phreatic eruptions or eventually to hazardous magmatic eruptions".
People are not allowed to stay within a six-kilometre "permanent danger zone" of the volcano, known for its near-perfect cone shape, following the "phreatic or steam-driven eruption", Phivolcs said.
Mayon, one of the most active volcanoes in the country, first spewed ashes, which reached 2.5 kilometers (1.5 miles) in a phreatic eruption, lasting for nearly two hours on Saturday afternoon.
The phreatic or stream-driven eruption of Mayon Volcano in Legazpi, Albay started at 4:21 p.m. Saturday, which lasted for an hour and 47 minutes.
It was followed by rumbling sounds and a faint glow in the crater, Phivolcs said.
"In case of ash fall events, which are most likely to affect communities on the western and southwestern flanks downwind of Mayon's crater, people should cover their nose and mouth with damp, clean cloth or dust mask", PHIVOLCS said.
Mayon's biggest eruption was in 1841, when lava flows buried a town, killing 1,200 people.
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It last erupted in 2014, spewing lava and forcing thousands of people to evacuate.
In its notice-to-airmen (notam) on Sunday, the Civil Aviation Authority of the Philippines (CAAP) said the "existence and horizontal/vertical extent of volcanic ash cloud" may endanger all aircraft passing near the area and advised against flying close to the summit.
It was not immediately clear how many residents had to leave the danger zone.
"Strictly no farming and orchid picking inside the 6-km PDZ, residents within the slope of the volcano experiencing heavy ashfall should take precautionary measure against possible roof collapsed due to accumulated heavy ash and rain", the advisory said.
'We could not see the extent of the ashfall due to thick clouds enveloping Mount Mayon, ' said Cedric Daep, chief of the provincial emergency management office.
"The volcano's abnormal behaviour began late a year ago and it seems due for another one", Phivolcs chief Renato Solidum said.