Manila, March 2 -- An increase in seismic activity has been observed in Bulusan Volcano, the Philippine Institute of Volcanology and Seismology (Phivolcs) said Monday.

In an advisory, the Phivolcs said there were 49 volcanic earthquakes since 3 a.m. of Feb. 26 until 11 a.m. of March 2. Of these, 16 were volcano-tectonic earthquakes associated with rock fracturing between three to six kilometers beneath the northern and southeastern edifice of the volcano.

The increased seismicity may indicate that hydrothermal processes beneath the volcano are underway and may lead to sudden steam-driven or phreatic eruption, Phivolcs said.

"This happens when there is an interaction with water and hot volcanic materials, which can cause rock fracturing...