Almost all of the 47,000 residents living on the slopes of a rumbling volcano in the central Philippines have moved to emergency shelters, and lava and earthquakes Tuesday heralded what officials say could be a major eruption.
Low clouds obscured visibility of the smoldering 8,070-foot (2,460-meter) Mayon, towering over coconut farms and rice paddies in coastal Albay province.
"Hazardous eruption ... can happen today or in the next few days," said chief state volcanologist Renato Solidum, adding that an eruption also may not happen. "Nobody has a 100 percent accuracy."
Ash columns were seen rising during a cloud break and Solidum said his team recorded 1,266 volcanic quakes in the last 24 hours, down from nearly 2,000 the previous day. He said that while the quakes were fewer, they were larger.
The emission of sulfur dioxide _ an indication of magma rising inside the volcano _ was measured at 6,530 tons per day, slightly less than 7,000 tons on Sunday, but still very high, Solidum said. The normal gas emission is 500 tons per day.
"Technically, Mayon volcano is already erupting because lava has oozed out," said Mahar Lagmay, professor of geological studies at the University of the Philippines. A bigger, explosive eruption is still possible but hard to predict, he said.
In the past week, more than 45,000 residents living in a five-mile (eight-kilometer) zone around Mayon have been transported in army trucks to school buildings and gymnasiums in and around the provincial capital of Legazpi, where they were given sleeping mats and food supplies to last them through Christmas holidays, said Jukes Nunez, a disaster management official.
Some of about 2,000 remaining farmers and their families living on the edge of the exclusion zone have already evacuated their homes three times but keep on returning to check on their livestock and vegetable farms, Nunez said.
Army troops and police were patrolling inside the danger zone to persuade the holdouts to move to a safe distance. Authorities said they were working on an evacuation center for farm animals.
Scientists have raised Mayon's alert level to one step below a hazardous eruption. The only higher level is when a major eruption is in progress. Red hot lava flows had reached three miles (five kilometers) from the crater accompanied by booming and rumbling sounds, said the Philippine Institute of Volcanology and Seismology.
Experts fear a major eruption could trigger pyroclastic flows _ superheated gas and volcanic debris that race down the slopes at high speeds, incinerating or vaporizing everything in their path. More extensive explosions of ash could drift toward nearby towns and cities, including Legazpi, about nine miles (15 kilometers) away.
In Mayon's other eruptions in recent years, pyroclastic flows had reached up to four miles (six kilometers) from the crater.
"The probability of survival in an eruption is zero if you're in the danger area. The solution is obviously distance," Albay Gov. Joey Salceda said.
Mayon has erupted nearly 40 times over 400 years. About 30,000 people were moved during the last eruption in 2006. An eruption in 1993 killed 79 people.
The first recorded eruption was in 1616; the most destructive came in 1814, killing more than 1,200 people and burying a town in volcanic mud. The ruins of the church in Cagsawa have become a tourist attraction.
In 1991, Mount Pinatubo exploded in the northern Philippines in one of the biggest volcanic eruptions of the 20th century, killing about 800 people.
Associated Press writers Teresa Cerojano, Jim Gomez and Hrvoje Hranjski in Manila contributed to this report.