The 8,118-foot-high mountain, famous for its near-perfect cone, Mayon volcano started spilling lava and debris in what some volcanologists said was the beginning of a silent eruption.

The increase in seismic activity itself did not warrant raising the alert level from two notches below the highest. Officials have estimated a hazardous eruption could happen within weeks.

Authorities extended a 3.7-mile danger zone around the peak of the volcano to four miles on the southeastern slope, where most of the lava and other debris has been rolling down.

On the streets of Legazpi city, the capital of Albay province near the volcano, about 210 miles southeast of Manila, residents watched boulders and other debris cascading from the crater, raising brownish-gray clouds of dust.

Mayon’s most violent eruption, in 1814, killed more than 1,200 people and buried a town in mud. A 1993 eruption killed 79. An eruption warning system is already in place for the quick evacuation of nearby communities, and radio stations have been told to broadcast emergency calls, said Jukes Nunez, an operations officer with the provincial disaster officer.

The Philippines is in the Pacific “Ring of Fire,” where volcanic activity and earthquakes are common.