A tangle of cracks has opened up around an erupting volcano in the Philippines that has triggered hundreds of earthquakes and urgent pleas for residents to evacuate areas at risk of dangerous fissures and ashfall.

Police locked down three towns near Taal Volcano, 40 miles south of Manila, to prevent residents from returning home. More than 82,000 people are in shelters, said the head of the military’s task force on Taal. Still, thousands have refused to leave their homes or have drifted back, even as the volcano spews ash and debris.

More areas are being considered to be placed under lockdown, the military said. Soldiers and police were also deployed to patrol vacated areas to prevent looting.

“Hazardous explosive eruption is possible within hours to days,” the Philippine Institute of Volcanology and Seismology said, repeating warnings since Sunday, when Taal entered a period of intense unrest.

New cracks were observed in a dozen towns, along with the drying up of portions of the nearby Pansipit River, the agency said. Satellite images showed that the main crater lake has been drained and new vent craters have formed, it said.

That’s a sign that magma could be rising from underground, agency chief Renato Solidum said. Taal Volcano, which lies in the middle of a lake, is a tourist attraction and is among the nation’s most active volcanoes.

A 65-year-old woman died Monday of cardiac arrest during an evacuation of Talisay, the Office of Civil Defense said Wednesday.

Dark, steam-laden plumes have risen above the main crater, and the eruptions precipitated 53 volcanic earthquakes in the 11 hours through 4 p.m. Wednesday, adding to the hundreds reported this week, the volcanology agency said.

“Such intense seismic activity probably signifies continuous magmatic intrusion beneath the Taal edifice, which may lead to further eruptive activity,” the agency added.

Crop damage from the eruption, including rice, corn, coffee, cacao and bananas, has reached $11.4 million, the Agriculture Department said. Mass fish deaths are expected in the lake surrounding the volcano.

It’s difficult to predict how long the volcano could remain at this level of activity, said Mario Aurelio, director of the National Institute of Geological Sciences at the University of the Philippines. Previous eruptions suggest it could persist for weeks to months, he said.

“This eruption is unlike before,” said 80-year-old Lucia Masambique.

She and her family of 20 are taking refuge in a school in the inland city of Santo Tomas in Batangas — their second move since the eruption. They will have to transfer again by Saturday because students will need the rooms for exams.