LEGAZPI CITY, Philippines--The Philippine Institute of Volcanology and Seismology is keeping a tight watch over Mayon volcano after it monitored a mild explosion in the mountain at 9:12 a.m. Sunday, a Phivolcs bulletin at noontime said.

Mt. Mayon emitted smoke that reached a height of around 200 meters above the summit, said the Phivolcs bulletin. The smoke from the volcano summit later drifted east northeast.

"The volcano is undergoing an episode of increased activity probably related to magma movement and though no major eruption is indicated, steam and ash explosions may occur in the following days," added the bulletin.

The Phivolcs reiterated that Alert Level 1 remained over Mt. Mayon as of Sunday. It has also reminded the public that the seven-kilometer extended danger zone at the southeastern flank and the six-kilometer permanent danger zone at other areas remain off-limits due to threats from sudden small explosions and rockfalls from the upper slopes.