The Philippine Institute of Volcanology and Seismology (PHILVOCS) said a deafening noise was reported at 9.15 a.m.
Ash from the steam-triggered eruption hit as high as two km, Xinhua news agency quoted an official Renato Solidum as saying.
Volcanic ash has fallen in the towns of Casiguran and Juban, located at the foot of the volcano.
Troops will evacuate some 1,000 residents from these two towns, according to army officer Lt. Col. Santiago Enginco.
Mt. Bulusan is the highest peak in Sorsogon and covers a land area of 3,672 hectares.
The volcano began spewing ash and steam in December last year.
Authorities have advised pilots not to fly close to the volcano's summit.
Deccan Herald is on WhatsApp Channels| Join now for Breaking News & Editor's Picks