LEGASPI CITY, Philippines- More than 3,000 villagers remaining in a no-go zone around the Philippines' rumbling Mayon volcano on Monday began to evacuate after officials threatened to force them out.

Scientists warned that powerful booms emanating from the Southeast Asian country's most active volcano, located about 330 kilometers (200 miles) southeast of Manila, indicated that a major eruption was imminent.

In Guinobatan village, lying on a dirt road in the foothills of Mayon, district officials and police went house-to-house, urging residents to board a truck and take shelter outside the danger zone, an AFP photographer saw.

Nearly all the villagers calmly boarded the hired truck, carrying their personal belongings in sacks and heading to evacuation centres set up by authorities outside an eight-kilometer radius.

But some of the men refused to budge and were left alone to fend for themselves.

"There are still one or two men who don't want to go but their families have come down to the evacuation centers," village councillor Mulad Bucad told AFP.

"There are always a few who don't want to go. They say they are used to eruptions and they never get hurt anyway," he said.

The eerie glow of crimson lava could be seen oozing from the volcano overnight, and the Philippine Institute of Volcanology and Seismology said seismic activity had "increased in number and size".

It said a total of 1,942 volcanic quakes were detected since Sunday, while sulfur dioxide emissions were "very high".

Albay Governor Joey Salceda earlier Monday said authorities "will physically remove" those refusing to leave the danger zone after volcanologists raised the alert level to four on a five-point scale.

Level four means that an "explosive eruption is possible within hours or days", according to the institute.

There were still 729 families or more than 3,000 people staying put on the edges of the danger zone, local disaster preparations chief Cedric Daep told AFP earlier.

Just over 9,200 families or nearly 44,400 people had already taken shelter in the evacuation centers since Mayon started belching ash, steam and lava last week.

If the alert level is raised to five, meaning that an eruption is in progress, another 16,000 villagers living beyond the danger zone will also have to be evacuated as a precautionary measure, Salceda said.

International aid began arriving in the province Monday, with the UN Children's Fund handing out medical and sanitary kits to thousands now crammed into about 24 schools converted into evacuation centers.

Huge tents were to be delivered soon to ensure that about 24,000 children whose classes have been interrupted because of the evacuation would be able to resume their studies after the Christmas break, it said.

Scientists said there has been an increasing frequency of booms from inside the volcano, which can be heard as far as 12 kilometers away.

"We cannot say exactly when the hazardous eruption is likely to occur," chief government volcanologist Renato Solidum said in a television interview.

But he stressed: "The important thing is the distance from the volcano. That is why it is important that people not be inside the danger zone."

Mayon oozed lava and vented steam for two months when it last erupted in 2006. No one was killed by the eruption itself.

But three months later, a powerful typhoon dislodged tons of volcanic debris that had collected on Mayon's slopes. The avalanche of mud and boulders crushed entire villages, leaving more than 1,000 people dead.

The 2,460-metre (8,070-foot) volcano, which is famed for its near-perfect cone, has erupted 48 times in recorded history. In 1814, more than 1,200 people were killed as lava buried the town of Cagsawa.