MANILA, Philippines — Philippine officials on Thursday raised the alert level for one of the country’s most active volcanoes after superheated streams of gas, debris and rocks cascaded down its upper slope in a condition they fear could lead to a hazardous eruption within days or weeks.

Villagers living within a 6-kilometer (3.7-mile) radius of Mayon volcano’s crater were told to leave the long-designated permanent danger zone and move to safer grounds due to the danger of volcanic emissions, lava flows, rockfalls and other hazards, officials said.

“Civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden eruption can be hazardous to aircraft,” the Philippine Institute of Volcanology and Seismology said.

A tourist draw in northeastern Albay province for its picturesque conical shape, Mayon is one of the most restive of two dozen active volcanoes across the Philippines. It last erupted violently in 2018, displacing tens of thousands of villagers.

Government volcano experts said they raised the alert level around Mayon to the third of a five-step warning system after detecting an increasing number of rockfalls and at least two volcanic earthquakes in recent days. Three brief volcanic gas and ash emissions on Thursday streamed down the volcano’s southeastern gully about a kilometer (half a mile) from the crater, they said.

“This means that Mayon is exhibiting magmatic eruption of a summit lava dome with increased chances of lava flows ... and of potential explosive activity within weeks or even days,” the government volcanology institute said.

Aside from Mayon, officials were closely monitoring Taal volcano south of Manila and Mount Kanlaon on central Negros island due to renewed signs of restiveness.

A number of villages in three towns near Taal suspended classes on Wednesday due to thick smog emanating from the volcano, one of the world’s smallest, and residents were advised to limit outdoor activities and wear masks for protection.

The Philippines lies along the Pacific Ring of Fire, a region prone to earthquakes and volcanic eruptions. A long-dormant volcano, Mount Pinatubo, blew its top north of Manila in 1991 in one of the biggest volcanic eruptions of the 20th century, killing hundreds of people.