It was the latest in a series of ash explosions that have raised fears that 1,565-meter (5,134-foot) high Mount Bulusan, on the southern tip of Luzon island, might be ready to erupt.

Radio reports from the scene said a loud explosion had been heard from the crater and that the falling ash had turned vegetation, houses and even cattle around the volcano, white.

However there were no immediate reports of casualties or damage.

The ash explosion was not preceded by volcanic quakes and may just be the result of hot rocks coming into contact with groundwater, said Julio Sabit of the Philippine Institute of Volcanology and Seismology.

He said that more explosions were expected but would not say if the volcano might erupt.

Authorities have set up a six-kilometer (four-mile) danger zone around the volcano where no one is supposed to enter. The volcano has been periodically ejecting ash into the sky amid a greater frequency of volcanic quakes in recent days.

Mayor Edwin Hamor of the nearby city of Casiguran, said 42 families who lived near the volcano were being evacuated to a local school after ash fell on their community.

Experts have warned that a major eruption could threaten the lives of at least 20,000 people in a "worst-case scenario."

Bulusan is one of the most active of the 22 volcanoes that have erupted within recorded history in the Philippines. It has erupted 15 times, most recently in November 1994.

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