Vulcanologists have warned the picturesque mountain in the centre of the country could blow at any time and the authorities have ordered all 35,000 nearby residents to leave their homes immediately.

The volcano is the most active in the Philippines and has erupted around 50 times in the past 400 years, often with deadly consequences. It has been rumbling since February and started spewing lava last month.

So far around 23,000 of the estimated 35,000 people who live around the volcano have been evacuated in military trucks to government-run shelters, said Glenn Rabonza, head of the civil defense office in Manila.

The government ordered the mandatory evacuation on Monday after repeated crater explosions shot giant clouds of smoke and ash billowing into the skies above the mountain.

The volcano was quiet on Tuesday morning and its cone-shaped summit obscured by clouds.

The Philippines state's chief vulcanologist Ernesto Corpus warned the volcanic eruption was now entering a far more dangerous phase that could involve sudden and violent explosions of volcanic rock, ash and fumes.

"It is absolutely clear to us that Mayon will blow. What we're seeing now is the shift in its activity from a quiet eruption to a more explosive activity," Corpus said.

However, he said that for as long as the communities around the scenic mountain followed the government's evacuation orders, the physical and economic fallout would be limited.

The government wants to implement a "no human activity zone" within eight kilometers (five miles) of the crater, and provincial governor Fernando Gonzalez said he hoped the evacuation would be completed Tuesday.

A brigade-sized military unit of several thousand soldiers and a fleet of 80 military trucks are enforcing the evacuation.

However several farmers on the slopes of the volcano told AFP they would not leave their homes until the situation became more serious.

Bienvenido Belga said he and about 10 neighbors were remaining on Mayon's slopes staying in a hut while they harvested their crop of copra, dried coconut meat. He said they did not feel in danger yet.

"We need the money. The copra will rot if left there," he said. "We still have six sacks to bring down."

Ed Laguerta, head of the Mayon volcano monitoring team, said volcanic quakes beneath the crater had been increasing, followed by minor ash explosions that indicate "more pressure inside the volcano."

"In our experience, when these signs can be seen, it might take several days, within a week, before a hazardous eruption can occur."

Laguerta said the lava column that began streaming out of the crater more than three weeks ago was now just two kilometers (1.24 miles) from inhabited areas.

But he said it was contained within two channels and was no threat to people, although it was burning coconut plantations.

He said the greatest danger would be from so-called "pyroclastic flows" or the superheated ash and other volcanic material that spurt from the crater and flow down the mountain's flanks at great speed.

He said these flows killed 77 people, mainly farmers, in Mayon's last deadly eruption in 1993.

Mayon has erupted 47 times since records began being kept in 1616. The deadliest eruption came on February 1, 1814, when Mayon spewed masses of lava that buried the town of Cagsawa and killed an estimated 1,200 people.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.