ALBAY CITY -- One of the country's most active volcanoes shot up an ash plume Wednesday, prompting hundreds of nearby residents to evacuate in case of an eruption.

Chief state volcanologist Renato Solidum said the alert level remains the same at the cone-shaped Mayon volcano, which killed several people in an eruption 16 years ago. He added, however, that if magma continues to rise below the glowing crater, there could be another eruption within weeks.

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Two explosions around 1 a.m. Wednesday sent ash and rocks more than half a kilometer into the air.

A thin layer of ash fell on the nearby towns of Camalig, Guinobatan and Ligao on Mayon's southwestern foothills.

Solidum said the explosions occurred at the summit crater of Mayon and were recorded by the seismic network as explosion-type earthquake that lasted for about three minutes. The explosions were accompanied by rumbling sounds.

The Philippine Institute of Volcanology and Seismology (Philvolcs) said in its bulletin Wednesday that incandescent rock fragments at the upper slope were observed in Barangay Lidong of Sto. Domingo, Barangays Tumpa and Anoling of Camalig.

Ash column was not observed due to cloud cover. However, field investigation conducted after the explosions showed that ashfall drifted towards the southwest quadrant of Mayon volcano due to the prevailing northeast monsoon.

The villages affected by traces of ashfall were Barangay Tumpa of Camalig, Barangays Travesia, Maipon, Masarawag, Doña Tumasa, Muladbukad Grande, and Pequeño of Guinobatan, Barangays Nabonton and Nasisi of Ligao.

Light ashfall, the Phivolcs reported, was also noted at Barangay San Rafael of Guinobatan.

In Daraga town, south of the volcano's crater, Mayor Cicero Triunfante ordered the early evacuation of more than 800 residents in the villages of Matnog and Banadero on fears that it might be in the path of superheated volcanic debris called pyroclastic flow.

Elsewhere in Bicol Region, officials distributed wireless public address systems to more than 700 village and town officials to help them make emergency evacuation announcements if necessary, said provincial disaster officer Cedric Daep.

He said mass evacuations would be ordered once the Phivolcs raises the alert on Mayon volcano to the next higher level. At present, Mayon is on alert level 2.

About 30,000 people were evacuated when Mayon last erupted in 2006, and for the past 24 hours, the seismic network recorded twenty volcanic earthquakes.

Officials repeated warnings over radio stations early Wednesday against mountain climbing, gathering orchids, farming and other "human activities" on the slopes of the 8,070-foot (2,460-meter) volcano, Daep said.

The Phivolcs, on its website, also strongly recommends that the six-kilometer radius Permanent Danger Zone (PDZ) around the volcano and the seven-kiometer Extended Danger Zone (EDZ) on the southeast flank of Mayon are off-limits due to the threat from sudden explosions and rockfalls from the upper slope.

Active river channels and areas perennially identified as lahar prone in the southeast sector should also be avoided, especially during bad weather condition or when there is heavy and prolonged rainfall, the Phivolcs added.

In case of ashfall, residents in affected areas were advised to stay inside their houses or cover their nose with clean wet cloth or dust mask.

Resident volcanologist Ed Laguerta said ground measurements showed that the upper slopes of Mayon were slightly inflated, indicating the presence of rising magma, and that minor ash explosions are to be expected.

He said hourly measurements were being taken.

Mayon's most violent eruption, in 1814, killed more than 1,200 people and buried a town in mud. A 1993 eruption killed 79 people.

Typhoon-triggered mudslides near the mountain in 2006 buried entire villages, killing more than 1,000 people.

The Philippines is in the Pacific "Ring of Fire," where volcanic activity and earthquakes are common. (AP/Sunnex)