Disaster officials in the central province of Albay are trying to move 35,000 people from an 8km danger zone on the southeast flank of Mayon on Tuesday.
The most active of the country's 22 volcanoes has been belching ash and lava since July, and the Philippine Institute of Volcanology and Seismology says it could erupt at any time.
Renato Solidum, the government's chief vulcanologist, said the institute had recorded 108 earthquakes inside Mayon over 24 hours and the crater had belched more than 12,000 tonnes of sulphur dioxide gas, more than double normal levels.
"This would indicate that new and gaseous magma is moving up towards the surface of the volcano and this might enhance the possibility of triggering a hazardous explosive eruption," he said.
Around 25,000 people have been evacuated but some villagers are refusing to abandon their livestock and vegetable plots for crowded schoolhouses, where families are being given shelter while they wait for Mayon to explode.
Local officials and soldiers appealed to stragglers to leave the danger zone.
"Are there still people out there? All of you evacuate now," a soldier with an automatic rifle shouted through a megaphone in one village.
Arroyo has urged residents 'not
to flirt with danger'
Disaster officials have said that police and soldiers will forcibly remove people who refuse to leave voluntarily.
Gloria Macapagal Arroyo, the president, urged residents "not to flirt with danger" and said evacuation centres were prepared to offer basic needs and services.
"We are confident of achieving a zero-casualty toll in this looming natural disaster," she said in a statement.
Mayon has erupted around 50 times over the past four centuries, most recently in 2000 and 2001.
The most destructive eruption was in 1841 when lava flows buried a town and killed 1,200 people.
At Albay Central Elementary School, conditions were cramped with 15 families sharing one classroom and mothers forced to wash their children in buckets in the playground.
Gloria Carasog said she had fled her village with five grandchildren.
"There are so many people here," she said, a small girl in her arms. "We are suffering."
A four-storey wall of lava has pushed to within 2km of some villages.
Vulcanologists fear farmers will be unable to outrun the molten rock and flying boulders if Mayon erupts.
At night, locals go to observation points outside the danger zone to drink beer and watch the pyrotechnic spectacle.
The Philippines lies on the "Ring of Fire", a belt of volcanoes around the Pacific Ocean that is also prone to earthquakes.