MANILA, Philippines — The cone-shaped Mayon volcano in the central Philippines, which killed scores in an eruption 16 years ago, shot up an ash plume Wednesday -- prompting hundreds of nearby residents to evacuate in case it blows again.

Chief state volcanologist Renato Solidum said the alert level remains the same at Mayon, the country's most active volcano, but that if magma continues to rise below the glowing crater there could be another eruption within weeks.

In Daraga township on the southern slope of the mountain, Mayor Cicero Triunfante ordered the early evacuation of more than 300 residents in the village of Matnog on fears that it might be in the path of superheated volcanic debris called pyroclastic flow.

Elsewhere, 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 Philippine Institute of Volcanology and Seismology raises the alert to the next higher level. About 30,000 people were evacuated when it last erupted in 2006.

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

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. Hourly measurements were being taken, he added.

Two explosions early Wednesday sent ash and rocks more than half a kilometre into the air. A thin layer of ash fell on the nearby towns of Camalig, Guinobatan and Ligao on Mayon's southwestern foothills.

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.