MANILA -- Philippine authorities on Monday raised the alert level for Mount Bulusan after the volcano in Sorsogon province, southeast of Manila, spewed a dark plume 4.5 km into the sky.

The Philippine Institute of Volcanology and Seismology raised the alert level from zero to one on a scale of five, or from normal to low-level unrest, after a phreatic eruption occurred at 4:36 am local time, which lasted 24 minutes.

"The event produced a bent plume that rose 4.5 km above the crater before drifting west to southwest," the institute said in an advisory, adding that ashes blanketed villages around the volcano.

The institute said the volcano produced "rumbling sounds" approximately 15 minutes before the eruption.

The institute warned of "chances of phreatic eruptions," urging villagers to be vigilant and prohibiting them from entering the 4 km danger zone of the volcano.

The institute also advised pilots and civil aviation authorities to avoid flying close to the volcano's summit.

There are 24 active volcanoes in the Philippines. Aside from Mount Bulusan, Mount Mayon in Albay province and Taal volcano near Manila are on alert level 1, while Mount Kanlaon is on alert level 3, or magmatic unrest, meaning there's an increased chance of a hazardous eruption, including explosive activity, lava flows, and pyroclastic density currents.

Located in the Pacific "Ring of Fire" region, the Philippines is prone to volcanic eruptions, earthquakes, and powerful typhoons.