Philippine officials have authorized the forcible removal of thousands of people reluctant to leave their farms near the smouldering Mayon volcano, which continues to spew lava and ash.

The governor of Albay province, Joey Salceda, said a provincial board has given security forces the go-ahead to move some 2,000 families who remain within an eight-kilometre danger zone around Mayon.

State volcanologists raised the alert level on Wednesday for the cone-shaped, 2,460-metre Mayon volcano to two steps below a major eruption, saying the activity could get worse in the coming days.

More than 33,000 of the 47,000 residents within an eight-km radius of Mayon have already been evacuated. A round-the-clock ban on returning to the area was also imposed on Thursday.

Salceda said police will show pictures of a 1993 eruption that killed more than 70 people in their effort to convince residents to leave peaceably.

Residents have been reluctant to leave their vegetable farms because the volcanic activity comes during harvest time.

Potential for eruption

Chief state volcanologist Renato Solidum said the volcano has caused 82 quakes and eight ash explosions during a 24-hour period ending Thursday morning.

Lava continues to trickle down the slope of the mountain on Thursday, and two domes of lava have built up inside the crater without cascading down the slopes. Solidum said these domes could grow larger and plug the crater.

"It can block the passage of gas. So then if the gas is pressurized, then it can explode," he said.

Mayon has erupted about 50 times over the last few hundred years, making it the most active volcano in the country. An eruption in 1814 killed 1,200 people.

More recently, the volcano spewed ash and lava from July to October 2006, sending about 30,000 people fleeing from their homes. In December 2006, typhoon-triggered mudslides along Mayon's slopes buried entire villages, killing more than 1,000 people.