On Sunday morning, Phivolcs said two more steam-driven ash explosions were recorded, producing grayish steam and ash plume.
Phivolcs raised the alert to level 2, then tweeted a statement late last night raising it to level 3, which means an "increased tendency to hazardous eruption".
"Since the eruption, rockfall events have been intermittently recorded" while a "faint crater glow" was detected late Saturday night.
Residents of the areas are also advised to wear face masks due to ash fall.
The volcano's most recent deadly activity came in 2013 when it suddenly spewed clouds of ash, killing five climbers.
He said not all residents evacuated live inside the 6-km danger zone.
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.
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This is the second phreatic eruption of Mayon which was recorded following a similar phenomenon which lasted for nearly two hours on Saturday afternoon.
Thousands of people have been forced into emergency shelters by an active volcano in the Philippines, with warnings a "hazardous eruption" could happen in days.
"The public is strongly advised to be vigilant and desist from entering the 6k-radius Permanent Danger Zone to minimise risks from sudden explosions, rockfall and landslides", Phivolcs said.
Dr Renato Solidum, the chief of the Philippine Institute of Volcanology and Seismology (Phivolcs), reported that Mount Mayon located in Albay province inthe Bicol Region, first erupted on Saturday afternoon, spewing ash and smoke in the air that lasted for one hour and 45 minutes.
Sto Domingo town mayor Herbie Aguas, on the other hand, ordered that residents within the slopes of the volcano who might be experiencing ashfalls should take precautionary measures against inhalation and possible roof collapse due to accumulated heavy ash and rain.
According to Solidum, Mayon appeared due for another eruption since it has been displaying abnormal behaviour since late previous year. In an 1814 eruption, roughly 1,200 people were killed and three towns were buried under mud and rock.
"We call on the people directly affected by the eruption of Mt Mayon to cooperate with their respective LGUs (local government units) in order for us to avoid injuries or casualties", Presidential Communications Secretary Martin Andanar said.