MANILA, June 1 (Xinhua) -- The Philippine Institute of Volcanology and Seismology on Thursday warned of a possibility of steam-driven eruptions at Bulusan Volcano in Sorsogon province, on southeastern tip of Luzon island.

The institute said it has recorded 18 volcanic earthquakes "associated with rock fracturing" from 5 a.m. local time on Wednesday, five of which were detected with depths of 2.71 to 6.56 kilometers beneath the eastern sector of the volcano.

The institute added that weak emission of white steam-laden plumes from the crater summit and active vents on the southeastern slopes could be observed.

"These parameters are likely related to volcanic gas activity within the edifice and may potentially trigger steam-driven or phreatic eruption from any active vents," the institute said.

The institute warned the people to stay away from a 4-kilometer radius danger zone. It further warned of the possibility of an eruption, rockfall, and landslide near the vents on the south-southeastern slopes.

The institute also asked civil aviation authorities to advise pilots to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be hazardous to aircraft.

Bulusan volcano, 70 kilometers away from the Philippines' most active Mayon volcano, spewed ash and steam into the sky in June last year, blanketing parts of the province with ash, forcing authorities to evacuate villagers.