The Philippines remained on alert Tuesday as authorities declared a "calamity zone" around Taal Volcano, which began spewing ash and lava over the weekend. They warned of indications that it could be on the cusp of a new, more powerful eruption.
Authorities said they feared the possibility of an event similar to the massive 1991 eruption of Mount Pinatubo, which killed hundreds and blanketed large swaths of the countryside, causing massive mudslides and large-scale economic hardship.
On Tuesday, Taal was spurting lava a half-mile into the sky along with a towering plume of volcanic ash — punctuated periodically by flashes of static lighting.
Since the eruption on Sunday, authorities have set the alert level at 4. Level 5, the highest, is reserved for an eruption in progress.
In hardest-hit Batangas province, the government declared a calamity zone — a move meant to smooth coordination between levels of government.
Forty miles to the north in Manila, a bustling city of 13 million was at a virtual standstill, with ash casting a gray pall over nearly deserted streets after businesses, schools and government offices were closed. The city's international airport, shut down on Monday, partially resumed flights on Tuesday after some 500 were canceled.
Taal, a popular tourist site situated on an island surrounded by a freshwater lake, sprung to life on Sunday, forcing the evacuation of some 30,000 people from a 9-mile radius around the volcano. Even so, that exclusion zone is home to about 560,000 people, and the effort to relocate them, amid the imminent threat posed by the volcano, appears to be far from complete.
Philippines Defense Secretary Delfin Lorenzana, who is also the head of the country's National Disaster Risk Reduction and Management Council, recalled that in the Pinatubo eruption, "the entire mountain collapsed."
"That's what we're fearing, that the eruption would cause the entire island to rise and scatter debris on the nearby areas," he said. "Hopefully this won't happen. We can never predict the actions of this volcano."
The Philippine Institute of Volcanology and Seismology reiterated its warning that an explosive eruption could happen in hours or days. It said there were several new fissures in the ground near the volcano — that, and about 50 volcanic earthquakes in an eight-hour period on Tuesday indicated that magma was rising underground and that another eruption was possible.
"The speed in the rise of magma is important (in determining) when the volcano will have a strong eruption and if it will slow down and freeze," the institutes's chief, Renato Solidum, said at a news conference Tuesday. "As of now, we don't see activities slowing down and the earthquakes still continue."
"We have to make sure that people understand and, of course, government, that this is not an activity that will just be [over] in a short while," Solidum said.
Authorities said that an eruption could also trigger a tsunami across the lake that surrounds the volcano.
Agoncillo and Lemery, two towns southwest of Taal, were coated in thick ash. The mayor of Agoncillo, Daniel Reyes, told DZMM radio that some of the town's buildings had collapsed under the weight of the ash accumulating on their rooftops.
The vice governor of nearby Talisay Batangas, Mark Leviste, was quoted by Reuters as saying the region had no power or water and that people were in need of face masks to protect them from the choking ash.
President Rodrigo Duterte is planning to visit the affected areas on Tuesday. He'll be wearing a portable air purifier when he arrives.
The Philippines lies at the edge of the Pacific "Ring of Fire," where seismic and volcanic activity due to the Earth's shifting plates are pronounced. Taal last erupted in 1977, one of some 30 times in the past five centuries. In 1911, an eruption killed 1,500 people.
NPR's Julie McCarthy in Manila contributed to this report.