MANILA - (3rd UPDATE) A lava dome in Mount Mayon collapsed twice early Monday, as thousands were evacuated along the path of the country's most active volcano, the Philippine Institute of Volcanology and Seismology said.

The 2 incidents of "lava collapse," observed at 9:41 a.m. and 10:05 a.m., sent into the sky plumes of grayish to white ash, Phivolcs research specialist Paul Alanis told ABS-CBN News.

In a message to ABS-CBN News, Phivolcs director Renato Solidum said: "Technically, Mayon has been erupting (non explosive magmatic eruption) with lava flow being issued out of the summit crater."

"Sometimes the lava piling up at the crater or lava flow on the upper slope would collapse and roll down the slope to generate a pyroclastic density current (pyroclastic flow) with ash cloud that one can see at the mid slopes causing ash fall. That was what observed," he added.

Monday's lava collapse brought ash fall in the towns of Camalig and Polangui, which lie on the southwestern flank of Mayon's crater, Alanis said.

Similar incidents and a "hazardous eruption" of Mayon are still possible in the "next weeks or days," he said.

Mayon remained under Alert Level 3, meaning "increased tendency towards hazardous eruption," Alanis said. The highest warning, level 5, means an eruption is ongoing.

Some 3,061 families or 12,044 individuals have been evacuated to nearby shelters, the national disaster agency said.

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.

Mayon, known for its near-perfect cone, last erupted in 2014. Its most destructive eruption was in February 1841, when lava flows buried a town and killed 1,200 people.

With reports from Agence France-Presse, Reuters and Jose Carretero and Karla Thea Omelan, ABS-CBN News