MANILA, Jan. 22 (Xinhua) -- The Philippine authorities raised the alert level for the Mayon volcano from level three to level four on Monday, meaning that a "hazardous eruption is imminent."

"Mayon volcano in Albay province has been exhibiting increased seismic unrest, lava fountaining and summit explosions," the Philippine Institute of Volcanology and Seismology (Phivolcs) said in its latest advisory.

Because of the volcano's intense unrest, the Institute extended the danger zone to 8 km radius from the summit vent.

Moreover, it urged pilots not to fly near the volcano's summit.

Renato Solidum, the head of Phivolcs, described Monday's eruption as "phreatomagmatic," meaning volcanic eruptions resulting from the interaction between magma and water.

Phivolcs upgraded the volcano to alert level four just a few minutes after the volcano suddenly erupted lava around noon on Monday.

Several hours before placing the volcano under alert level four, the Phivolcs indicated that 500-meter to 200-meter high lava fountains were generated at 10:45 p.m. local time on Sunday and 2:25 a.m. local time on Monday respectively.

According to Albay Governor Al Francis Bichara, all schools will be suspended in the whole province on Jan. 23.

Mountain Mayon, one of the Philippine most active volcanos famous for its beauty and near-perfect symmetry, is in Albay province on the Philippine main Luzon Island more than 300 km southeast of the Philippine capital Manila. It has an elevation of 2,462 meters.

In an 1814 eruption, more than 1,200 people were killed and three towns were buried under mud and rock.

Mayon volcano is a popular tourist destination in the Bicol region. It is famed for its near-perfect cone but has a long history of deadly eruptions. It has erupted 51 times during the last 400 years.