The Philippine Institute of Volcanology and Seismology (Phivolcs) on Tuesday night raised the alert for Bulusan Volcano to Level 1 (low level unrest).
Some 124 volcanic quakes were recorded since May 8. These quakes are caused by movements or eruptions of magma from the volcano.
Phreatic eruptions at the summit crater or flank vents from the upper to middle slopes were also observed.
Such parameters indicate that volcanic processes are underway beneath the edifice, Phivolcs said.
Phivolcs reiterated that entry into the four-kilometer radius permanent danger zone (PDZ) must be strictly prohibited.
Vigilance in the two-kilometer extended danger zone (EDZ) on the southeast sector must be exercised due to increased possibilities of sudden phreatic eruptions, it said.
It added that people living within valleys and along rivers must be vigilant against stream flows and lahar in the event of heavy rainfall. SOVEREIGNPH