LEGASPI CITY, Philippines - Thousands more Philippine villagers were evacuated from their homes on Wednesday as more lava poured out of the Mayon volcano and experts warned the crisis could go on for months.

As many as 50,000 people living in the foothills of the one of the country's most active volcanoes risk spending Christmas away from their homes with about 30,760 already evacuated by the authorities since Monday night.

At least 5 small explosions were detected from Mayon on Wednesday, one of of them shooting ash 500 metres (1,640 feet) into the air, government volcanologist July Sabit told AFP.

"Lava flow and lava fragments rolling down the volcano are continuous," Sabit said. "It is part of the eruptive activity of the volcano. There is a high probability it will be like this for months."

Sabit cited Mayon's last eruption in 2006, when it spewed ash and lava for two months and left huge deposits of ash on the slopes but did not claim any lives.

However, when Typhoon Durian hit the area in December 2006, it caused a landslide of volcanic ash that killed more than 1,000 people.

The government has since Monday night evacuated about 30,761 people from farming villages near the foot of Mayon and hopes to evacuate about 20,000 more this week, the civil defense office said.

Most of the evacuation centers are at government schools, where classes have been called off.

Raffy Valenzuela, the civil defense chief for Albay province, where Mayon is located, said the makeshift camps were not yet up to standard.

"Some (schoolhouses) don't have sufficient bathrooms, others have... no running water. We are still fixing these things because this evacuation has been very sudden," he said.

Chief volcanologist Renato Solidum said that in the "worst-case scenario" of a major eruption, the government might have to evacuate another 15,000 families, or roughly 75,000 people.

Military trucks and even heavy trucks intended for construction projects are being used to evacuate the residents, Solidum said.

The government is ready to forcibly evacuate all villagers within the danger zone but there has been no resistance so far, he added.

The Mayon threat has come at a particularly inconvenient time of the year for the evacuees as they, like most of the other 92 million people in the predominantly Christian country, prepare for Christmas celebrations.

Defense Secretary Norberto Gonzales, who is in charge of disaster preparations, conducted an aerial survey of the volcano using a military helicopter on Wednesday.

He promised to distribute thousands of face masks to villagers to protect them from the effects of any volcanic ashfall.

The Philippine Institute of Volcanology and Seismology raised the alert level for Mayon to 3 on Monday after lava was seen spewing from the crater, and evacuations began immediately.

Level 3 on the 5-point scale means a hazardous eruption is likely in the very near future. The institute said on Wednesday that alert level three remained in place.

Mayon, which sits above a farming area about 330 kilometers (200 miles) southeast of Manila, has erupted 48 times since records began, claiming thousands of lives.

In 1814, more than 1,200 people were killed as lava buried the town of Cagsawa.

However the 2,460-metre (8,070-feet) volcano remains a popular tourist attraction, and is famous for its perfect cone.

The Philippines is part of the so-called Pacific "Ring of Fire" that is known for its volcanic activity. The Philippine volcanology institute lists 22 active volcanoes in the country.