A two-day drive by the military and local government has seen 39,422 people evacuated from villages around the country's most active volcano which is showing strong signs of erupting, the provincial disaster coordinating council said.

President Gloria Arroyo late Wednesday declared the evacuation complete and successful, but warned residents against returning to their farms and homes until advised to do so by the government.

They must "heed the advice of experts and disaster officials to stay out of harm's way," she said, pledging that evacuees "will not be kept from their homes a minute longer than is necessary."

Officials said the main problem is dissuading residents from returning to their homes amid an apparent lull in the eruptive phase.

Throughout the day cloud shrouded the 8,070-foot (2,460-meter) volcano in the central Philippines as lava continued to flow slowly down its southeastern face.

The civil defense office in Manila said troops and police have set up checkpoints on Mayon's lower slopes to enforce a "No Human Activity" zone within eight kilometers (five miles) of the crater.

Farmers have been sneaking out of evacuation centers in the morning to work their farms on the fertile volcanic soil and guard their property.

Evacuation efforts were also complicated by communist guerrillas, who attacked an infantry unit evacuating residents near Daraga town close to the slopes of the volcano, the military said. Five soldiers were injured.

Relief agencies and residents are bracing for a long stay in makeshift evacuation centers, mainly schools.

"For the time being, food is not the problem," Legaspi City mayor Noel Rosal said, but appealed for help from the national government.

He said the effort could be sustained until the end of the week but if the evacuation drags on for weeks it will deplete the city's calamity fund.

It costs about 367,000 pesos (7,140 dollars) a day to feed and house the estimated 10,802 people sheltering in Legaspi's schools.

Arroyo on Wednesday ordered her budget department to prepare an extra 250 million pesos (4.86 million dollars) in calamity funds to augment the 76 million pesos earlier disbursed by the national government. She is expected to visit the area this weekend.

Schoolrooms are housing up to 30 evacuees who sleep on the cold concrete floor and are fed with tinned meat and instant noodles.

Local officials though are experienced in dealing with Mayon, which has erupted around 50 times in the past 400 years, most recently in 1993 when 77 people died.

The Philippine Institute of Volcanology and Seismology said that after an upsurge of activity on Monday the volcano was quieter on Tuesday and Wednesday.

From 109 volcanic quakes on Monday, only 21 were recorded on Tuesday. The amount of sulphur dioxide expelled also fell by nearly half. It has been quietly belching out lava since July 15.

However, the institute said such swings in activity were an anomaly and warned that a hazardous eruption could still take place within days.

"Anything above 500 tonnes (of sulphur dioxide emissions) is an indication" of volcanic unrest, said Ernesto Corpuz, head of the volcano monitoring division.

He noted that despite lower readings of sulphur emissions, a column of black, steaming lava was still oozing from the crater and snaking down a channel on its slopes.

This indicates lava is still pushing out toward the crater, which has been largely obscured by clouds since Monday.

Renato Solidum, head of the institute, said such swings in readings were "typical of Mayon" and stressed that they would not lower the alert level until they see about a week of lower volcanic activity.

He also warned that the "gravitational pull" of the full moon this week could trigger an explosive eruption.

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