SORSOGON CITY. Mt. Bulusan exploded yesterday morning, sending a thick ash column over five kilometers above its summit, the Philippine Institute of Volcanology (Phivolcs) here said.

It was a phreatic type of eruption characterized by a massive emission of volcanic ash accompanied by an explosion-type of earthquake detected by seismographs at the Phivolcs observatory at Barangay Cabid-an in this provincial capital.

Bella Tubianoza, resident volcanologist, said the eruption and explosion-type tremor occurred simultaneously and continuously, lasting for 10 minutes starting at 9:37 a.m.

The incident was considered the most significant activity of Mt. Bulusan since it started acting up last March although alert level one over the volcano was maintained, Tubianosa said.

"We expect a big bang but we do not know when it would come. Mt. Bulusan had this capability based on its history," she said.

The eruption was viewed in full at this city, over 30 kilometers from the volcano. While most residents were awed by the spectacular show of cauliflower-like column of ash, some panicked in fear.

But there is no cause for alarm even as residents near its foot should stay on alert for possible evacuation should the situation worsen into major eruptions, Tubianoza said.

Under the prevailing alert level, human activities are discouraged within the four to six-kilometer permanent danger zone of the volcano as major eruptions may take place without any warning, she added.