But many locals are still reluctant to leave the area, preferring to stay with their crops and belongings.

Officials have ordered the evacuation of thousands of people living near the volcano, in central Albay province.

The alert level was raised to four, the second highest level, as experts warned that an eruption could take place soon.

Mayon has been rumbling since February and started emitting lava in mid-July.

It is the most active volcano in the Philippines, having erupted about 50 times in the past 400 years.

'Everybody out'

Early on Monday, six successive volcanic blasts occurred within 40 minutes, sending ash up to 800m into the air.

By midday, Mayon's peak was covered in a dark cloud of volcanic material rising high above the crater.

Officials say residents will be forced to leave

Overnight the activity continued, with the volcano emitting ash at least three times, according to a vulcanologist who spoke to the Associated Press news agency.

Meanwhile the evacuation from the area is gathering pace.

Tens of thousands of villagers were taken by truck to 34 specially-created evacuation centres on Monday, but others still remain in the danger zone.

"Yesterday we evacuated 60%, but the evacuation is still ongoing until we take everybody out," Albay Governor Fernando Gonzales told Reuters news agency on Tuesday.

In total, 35,000 people will be moved from the area, and an additional 20,000 will be evacuated in the case of a major eruption.

Staying

Despite the mandatory evacuations, some villagers would rather stay on their farms, with their livestock and belongings.

Farmer Bienvenido Belga told the French news agency AFP: "We need the money. The copra (coconut meat) will rot if left there."

Even some of those who have been evacuated insist on returning regularly.

Eladio Petsalosi said: "I just came back to feed my cat... I will come back occasionally. I have a television at home. What if it gets stolen?"

Defence Secretary Avelino Cruz said that police would forcibly remove those who refused to leave.

"If we have to carry them out bodily into the truck and get them out of the zone, the Task Force Mayon will do that," he told a press conference on Monday.

The Philippines lies on the Pacific ring of fire, where volcanic activity and earthquakes are common.

Mayon is one of 22 active volcanoes in the Philippines. Its most violent eruption, in 1814, killed more than 1,200 people. Another 75 people died during an eruption in 1993.