The cone-shaped 2,462-meter (8,077-foot) volcano southeast of Manila has been spewing lava since last week and all signs indicate it was preparing for a major explosive eruption within days or weeks, volcanologists said.

"There were secondary explosions. A collapsed portion of the advancing lava caused an ash cloud of several hundred meters," scientist Ed Laguerta told AFP from the Philippine Institute of Volcanology and Seismology's observatory in Legaspi city near Mayon.

He said alert level three of a five-step alert system remained hoisted over Mayon and nearby towns and villagers, meaning that residents should prepare for eventual evacuation.

In the farming town of Matanag, which lies near the six-kilometer radius (four mile) permanent danger zone, residents have packed their things and were awaiting official word to evacuate.

"We only have one life to live each, it's important to save that," said coconut farmer Romeo Nantes, 55, and a father of three.

Nantes however said that he would be tending his farm until a major eruption occurs.

Under the shade of a tree, fellow farmer Balasta Balangitan, 37, led his family and friends in planning an escape route as they watched the smouldering lava flow snake down the slopes.

Balangitan said Matanag was among the towns devastated by Mayon's eruption in 2001, when several dozen people were killed.

Mayon, about 300 kilometers (176 miles) southeast of Manila, is one of some 22 active volcanoes in the Philippines.

It has erupted 47 times in recorded history, including in 1814, when it buried the town of Cagsawa killing an estimated 1,000 residents. Mayon's most recent major eruption was in 2001.