MANILA — The Philippines is bracing for a major eruption from one of its most active volcanoes amid escalating agitation Sunday that sent ash spewing as far as the capital and prompted the evacuation of thousands.

The column of ash released from the Taal volcano in Batangas province, almost two hours south of the capital, rose six to nine miles at around 5:30 p.m. local time.

Two hours later, the Philippine Institute of Volcanology and Seismology raised the alert status to Level 4, which means a “hazardous explosive eruption” was expected within hours to days. The highest alert, Level 5, is reserved for ongoing magma eruption.

The agency also warned that surrounding areas were at risk of a volcanic tsunami. A volcano can “displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area,” according to the International Tsunami Information Center.

“Waves will impact the coastline,” said Renato Solidum, director of the volcanology institute. “Sometimes, if there are boats or structures there, these can be destroyed.”

Tens of thousands were expected to evacuate from nearby cities and towns. The Philippine Red Cross deployed thousands of volunteers and at least nine ambulances in three surrounding provinces.

“Senior citizens must be taken care of, especially those with respiratory diseases,” said Richard Gordon, a senator who also serves as chairman of the Philippine Red Cross.

Ash clouded visibility on highways and coated cars and streets as far as Manila. Flights to and from the capital were canceled as ash accumulated on the runways. Drugstores quickly ran out of face masks.

From her home in Lipa City in Batangas, Kristienne Amante, 22, said the air smelled like sulfur “and there’s a constant rumble in the distance.”

She said her family had just evacuated from a lakeside municipality and had noted that there were only “minutes between quakes.”

Yvette Herras, 54, said her house in the town of Silang in Cavite province was in the danger zone. By the time she, her husband and three of their children left, there was no electricity or clean water.

“Our umbrellas are filled with mud,” Herras said. “It was scary. The air was orange [and] gray.

“We could hear explosions, thunder-like … We decided to leave because it was impossible to get out if we decide to go later.”

It took the family four hours to reach Manila, hitching a jeepney ride and then catching a bus. Herras said her daughter lives in the city, and they were spending the night with her.

“It’s still shocking for us,” she said. “When it erupted, we were watching a post-apocalyptic movie.”

According to the NASA Earth Observatory, Taal consists of multiple stratovolcanoes. Its primary feature is the three-mile-wide Volcano Island, which has 47 craters and sits in a lake.

The volcano has 33 recorded eruptions, the latest of which was in 1977.