Increased restiveness was recorded overnight, including 270 incidents of lava fragments and super-hot boulders rolling down from Mayon's crater — nearly four times the number recorded the previous day. Some reached the upper portion of a gully on the volcano's southeastern side, indicating that the lava dome has breached that side of the crater. The number of low-frequency volcanic earthquakes also increased.
Molten lava has accumulated at the top of the 2,460-meter (8,070-foot) volcano's crater, creating a glow in the night sky that sparked both awe and fear among spectators.
"It's already erupting, but not explosive," said Renato Solidum, who heads the government's volcano monitoring agency. "Currently, the activity is just lava coming down. If there is an explosion, all sides of the volcano are threatened."
Volcanologist Ed Laguerta said he saw huge glowing lava fragments and super-hot boulders rolling down from Mayon's crater late Tuesday from as far as 12 kilometers (7 miles) away.
"They are big because they can be seen from afar, and they splinter, so they could be car-sized," he added.
Mount Mayon, a popular tourist site known for its near-perfect cone, lies in coconut-producing Albay province, about 340 kilometers (210 miles) southeast of Manila.
The provincial disaster operations center reported Wednesday that nearly 24,000 people from villages within an 8-kilometer (5-mile) radius from the crater had been evacuated.
Mayor Herbie Aguas said his farming town of Santo Domingo, among the closest to the volcano, has a frightening legacy from Mayon. The volcano nearly wiped out the municipality's entire population in an 1897 eruption with pyroclastic flows — superheated gas and volcanic debris that race down the slopes at high speeds, vaporizing everything in their path.
"We are praying that it would not be the worst-case scenario," Aguas said, adding that nearly 4,000 of the 40,000 residents in his town who live within a government-declared danger zone had started to evacuate to safer areas.
The volcano has erupted 50 times in the last 500 years, sometimes violently, endangering thousands of poor villagers who insist on living or farming in the danger zone.
Villagers living near the volcano have erected huge white crosses at the entrance of their neighborhoods, hoping they will protect them from harm.
On May 7, 2013, the volcano suddenly spewed ash, killing five climbers, including three Germans, who had ventured near the summit despite warnings of possible danger.