(AP) -- The Philippines' most active volcano could have a huge eruption within days, officials warned Sunday after detecting a drastic surge in earthquakes and eerie rumbling sounds in surrounding foothills. Tens of thousands of villagers have been evacuated as a precaution.
Scientists raised the alert level for the Mayon volcano after 453 volcanic earthquakes were detected in a five-hour span Sunday, compared to just over 200 Saturday, said Renato Solidum, chief of the Philippine Institute of Volcanology and Seismology.
The five-step warning system was raised to level four, meaning a hazardous eruption "is possible within days." Level five is when a major eruption has begun.
Army troops and police will intensify patrols to enforce a round-the-clock ban on villagers moving within a five-mile (eight-kilometer) danger zone around the 8,070-foot (2,460-meter) mountain, said Gov. Joey Salceda of Albay province, about 210 miles (340 kilometers) southeast of Manila.
More than 40,000 villagers have been moved to school buildings and other emergency shelters, but some have still been spotted checking on their farms in the prohibited zone. Salceda said about 5,000 more villagers were being evacuated away from the volcano.
The cone-shaped volcano began emitting red-hot lava and puffing columns of ash last week. It belched a plume of grayish ash half a mile (nearly a kilometer) into the sky Sunday, and lava has flowed about 2.8 miles (4.5 kilometers) down the mountainside, Salceda said.
A major eruption can trigger pyroclastic flows - superheated gas and volcanic debris that can race down the slopes at very high speed, vaporizing everything in their path. There can be more extensive ejections of ash, which can drift toward nearby townships.
In Mayon's major eruptions in recent years, such pyroclastic flows have reached up to four miles (six kilometers) down from the crater on the volcano's southern flank - a farming region where most residents have been evacuated, Salceda said.
Army checkpoints have been set up and patrols have been intensified to ensure residents will not sneak back to check on their homes and farms, as some have done in recent days, Salceda said.
"I have set a very high bar, which is zero casualty," Salceda told The Associated Press. "If there's a lull and you step back into the danger zone, you'll immediately be escorted out."
The evacuations were unfortunate, coming so close before Christmas, but authorities will find ways to bring holiday cheer to displaced villagers in emergency shelters, he said.
He said residents are used to playing a "cat and mouse" game with Mayon, a popular tourist attraction because of its near-perfect cone shape.
Residents who briefly returned to their homes within the danger zone Sunday morning to check on their belongings reported hearing eerie rumbling sounds. Some were seen by journalists tending to their farms within the prohibited zone near Guinobatan township.
In 1991, Mount Pinatubo exploded in the northern Philippines in one of the world's biggest volcanic eruptions of the 20th century, killing about 800 people.
Mayon last erupted in 2006, when about 30,000 people were moved. Another eruption in 1993 killed 79 people.
The first recorded eruption was in 1616 but 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 an iconic tourist spot.
Explore further: 'Ice vault' idea to keep climate's time capsule intact