(this story corrects year of most destructive eruption to 1814.)

MANILA (Reuters) - The Philippines raised the alert level at its rumbling Mayon volcano to “level 3” on Sunday after detecting lava flow and indications of activity that could lead to eruptions of magma.

More than 900 families have been evacuated from villages near Mayon, a tourist attraction because of its near-perfect cone shape, following a “steam-driven eruption” on Saturday.

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.

Two similar “phreatic” eruptions occurred at the volcano in central Albay province on Sunday, unleashing more ash.

“Mayon’s summit crater is now exhibiting bright crater glow that signifies the growth of a new lava dome and beginnings of lava flow towards the southern slopes,” the Philippine Institute of Volcanology and Seismology (Phivolcs) said.

Phivolcs chief Renato Solidum said the volcano appeared due for another major eruption as it has been displaying abnormal behavior since late last year.

“Alert level 3 is what we considered critical, 4 is when eruption is imminent, and 5 is eruption in progress,” Cedric Daep, head of the Albay Provincial Disaster Risk Reduction and Management Office, said in a radio interview.

Mayon’s most destructive eruption was in February 1814, when lava buried a town and killed 1,200 people. It last erupted in 2014, spewing lava and forcing thousands of people to evacuate.

The latest eruptions began on Saturday, unleashing ash, rocks and sulfur fumes and accompanied by rumbling sounds.

Phivolcs had earlier raised the alert to “level 2”, saying the activity was “probably of magmatic origin, which could lead to more phreatic eruptions or eventually to hazardous magmatic eruptions.”

Since Saturday’s first eruption, Phivolcs said it had recorded 158 rockfall events and urged people to stay away from a 6-kilometre (3.7 mile) radius Permanent Danger Zone and a 7-km Expanded Danger Zone on the volcano’s southern flank.

Landslides and sudden explosions or a dome collapse that may generate hazardous volcanic flows are also possible, it said.

People within the slope of the volcano, but outside the danger zones, were told to take precautionary measures against possible roof collapses due to accumulated ash and rainwater, and “lahar”, an Indonesian term for a volcanic mudflow.

And the provincial government suspended Monday’s classes from kindergarten to senior high school in some areas.