MANILA   -   The alert level for a Philippine volcano was raised on Monday after an “explosive eruption” sent a plume of ash, gas and rocks five kilometres (three miles) into the sky, the volcanology agency said. Mount Kanlaon on the central island of Negros erupted for six minutes shortly before 7:00 pm (1100 GMT), prompting warnings for nearby residents to wear facemasks due the threat of volcanic gases and falling ash. “When it erupted we heard a thunder-like sound,” Ethan Asentista-Khoo, 35, told AFP from his home in Pula village, about six kilometres from the volcano. “There was like a fire on the mouth of the volcano, which lasted around one to two minutes. I didn’t see any lava or rocks coming out.” The Philippines is located in the seismically active Pacific “Ring of Fire” that hosts more than half of the world’s volcanoes. Kanlaon is one of 24 active volcanoes in the archipelago nation.  “An explosive eruption... produced a voluminous and incandescent plume that rapidly rose to 5,000 metres above the vent,” the Philippine Institute of Volcanology and Seismology said, raising the alert level from one to two on a scale of zero to five. It also observed “probable short” avalanches of volcanic ash, rock and gases, known  as pyroclastic density currents, on Kanlaon’s slopes. Joe Alingasa, a rescue official in San Carlos municipality, said they planned to evacuate about 500 families from homes nearest the volcano “as soon as possible”. “We have deployed a team for the initial evacuation of our residents,” Alingasa told AFP. “We also took face masks because the residents reported a strong smell of sulphur in the area.” The  volcanology agency said pilots should avoid flying close to the volcano’s summit as ash from a sudden eruption could be hazardous to their aircraft. Eruptions can be deadly, with pyroclastic and lahar flows as well as ashfall posing hazards to communities surrounding the volcano.  Pyroclastic flows are a scalding mixture of rocks and ash that speed down a volcano’s slopes, burning everything in their path. Lahars are mammoth flows of volcanic debris deposited on the volcano’s slopes and unleashed by heavy rain. They can bury villages. Heavy ashfalls can collapse roofs of houses and gum up jet engines. The most powerful volcanic explosion in the Philippines in recent years was the 1991 eruption of Pinatubo, about 100 kilometres from Manila, which killed more than 800 people.