The Philippines' Mayon volcano may be showing less visible signs of unrest but this could be a deceptive calm before a deadly eruption, the chief government volcanologist said on Sunday.

"Do not become complacent. The people only see what is coming out of the crater and that is often cloud covered. It is not just the observed phenomenon that matters. We also look at the quakes, the gas emitted and the swelling of the volcano," said chief volcanologist Renato Solidum.

"We are telling the people, 'do not just count the number of quakes or what you see from the crater.' It may look calm but it is not calm. It can still explode," he warned in a radio broadcast.

"You might think it is taking a break but the volcano is still swelling," he said after the restive volcano emitted fewer ash emissions on Sunday than in previous days.

He said that while the amount of lava trickling out of the volcano had fallen, the magma inside Mayon was still rising, possibly indicating that the volcano was clogged.

Mayon, the Philippines' most active volcano, located about 330 kilometres (200 miles) southeast of Manila, increased its activity earlier this month, prompting the government to put it under alert level four -- meaning that an explosive eruption could happen any day now.

Residents living in an eight-kilometre danger zone around Mayon have been evacuated despite some refusing to leave their farms.

More than 47,500 people have been taken to 29 evacuation centres to protect them from a possible eruption although some people are known to defy army security, sneaking out to periodically return home for supplies.

"Soldiers are continuously intensifying checkpoint operations and security patrols within the danger zones," said army spokesman Captain Razaleigh Bansawan.

Solidum warned that the volcano could stay active for as long as two months, similar to its last eruption in 2006 when it simmered for months, dumping tonnes of ash on its slopes.

No one was killed by the eruption itself but in December of that year a passing typhoon dislodged the ash from Mayon's slopes, turning it into a fast-moving mudflow that covered villages and killed about a thousand people.

The 2,460-metre (8,070-foot) volcano, which is famed for its near-perfect cone, has erupted 48 times in recorded history. In 1814, more than 1,200 people were killed as lava buried the town of Cagsawa.

earlier related report
'Clogged' Philippine volcano could burst: expert
Legaspi, Philippines (AFP) Dec 26, 2009 - Rumbling Mayon volcano in the Philippines is showing signs of becoming clogged with lava and could erupt explosively, a government volcanologist said Saturday.

The volcano, which has been oozing lava for weeks, is also emitting gas and ash, all signs of a powerful eruption any day now, said Ed Laguerta, head of the government's volcanology team monitoring Mayon.

"Mayon volcano is still in a high state of unrest and in the coming days it could still have an explosive eruption," he warned in a radio interview.

"The number of (volcanic) quakes have lessened but now the quakes are of a different variety. What is becoming clear is that it (the volcano) is getting clogged. That is when the lava is rising but cannot get out," he said.

"The edifice looks inflated so we cannot say that the actual activity of Mayon has decreased," he said.

"Just because the volcano looks calm... it does not mean its activity is decreasing. We cannot be off our guard. After this calm period, it could explode with even more force," Laguerta added.

The Philippine Institute of Volcanology and Seismology said it had kept Mayon on alert level four, meaning a hazardous eruption may occur within days.

It warned people to stay away from river channels and other areas that might possibly be hit by volcanic mudflow in the event heavy rain falls on Mayon.

The government has evacuated more than 47,000 people living around the volcano, about 330 kilometres (200 miles) southeast of Manila, since it began belching smoke and oozing lava earlier this month.

The evacuees are housed in 28 makeshift centres -- mostly government schools -- and could remain there for more than a month until the volcano settles, said Jukes Nunez, director of the disaster preparations office.

There are still a few people who refuse to leave the danger zone but Nunez said they were at the fringes of the zone and were not directly threatened.

However, he warned that the evacuees would need to find new shelters when schools reopen in January after the Christmas holidays.

Governor Joey Salceda, whose province includes Mayon, said in a television interview that he plans to set up a tent city for those who evacuated the area around the volcano.

The 2,460-metre (8,070-foot) volcano, which is famed for its near-perfect cone, has erupted 48 times in recorded history. In 1814, more than 1,200 people were killed as lava buried the town of Cagsawa.