MANILA - PHILIPPINE authorities warned on Friday that Mayon, one of the country's most active volcanoes, is showing signs of life and could erupt again soon.

The Philippine Institute of Volcanology and Seismology said it is raising the 2,460m mountain's alert status to 'moderate unrest' from that of 'low-level unrest.' Nearby residents were reminded not to venture into a 'permanent danger zone' in a 6km radius from the crater.

The zone was also extended to 7km on its south-east flank, which faces Legazpi, a city of 160,000 people.

'This alert condition signifies a state of unrest which could lead to ash explosions or eventually to hazardous magmatic eruption,' the institute said in its latest advisory.

The increased frequency of low-level volcanic quakes had pushed toward the crater lip 'a cone-shaped pile of hot, steaming old rocks, possibly remnants from previous eruptions which could be the source of the glow at the crater,' it added.

Seismologist Renato Solidum, the head of the government institute, said the immediate danger if volcanic activity escalates was of ash explosions that could affect aviation at Legazpi airport or crush roofs of nearby houses.

'Sudden explosions and rockfalls from the upper slopes' are also a threat, the advisory said.

Mayon has erupted 48 times since records began, most recently in 2006. A major eruption in 1814 buried the town of Cagsawa. -- AFP