Photo: Twitter

A volcano near the Philippine capital spewed lava into the sky and trembled constantly Tuesday, possibly portending a bigger and more dangerous eruption, as tens of thousands of people fled villages darkened and blanketed by heavy ash.

Government work was suspended and schools were closed in a number of towns and cities, including Manila, because of health risks from the ash. Hundreds of flights were cancelled or delayed, affecting tens of thousands of passengers.

The continued restiveness of the Taal volcano and several new fissures in the ground nearby likely mean magma is rising and may lead to further eruptive activity, the Philippine Institute of Volcanology and Seismology said.

The volcano was spurting fountains of red-hot lava 800 metres (half a mile) into the sky, and the massive column of ash and volcanic debris at times lit up with streaks of lightning.

The alert level since the eruption began Sunday has been 4, indicating a hazardous eruption is possible in hours to days. Level 5, the highest, means such an eruption is underway.

About 50 volcanic earthquakes were detected over eight hours Tuesday, indicating rising magma, the institute said. It also warned that heavy and prolonged ash fall was possible in nearby villages.

“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," said Renato Solidum, who heads the institute. "As of now, we don't see activities slowing down and the earthquakes still continue.”

The picturesque volcano in the middle of a lake in Batangas province south of Manila rumbled to life Sunday in a powerful explosion that blasted a 15-kilometre (9-mile) column of ash, steam and rock into the sky. Clouds of volcanic ash blowing over Manila, 65 kilometres (40 miles) to the north, closed the country's main airport Sunday and part of Monday until the ash fall eased.

More than 500 international and domestic flights were cancelled or delayed due to the overnight airport closure, affecting about 80,000 passengers, airport manager Ed Monreal told The Associated Press.

“Hopefully the wind direction does not change. As long as the ash fall does not reach us, then we can be back to normalcy,” Monreal said.

The disaster-response agency counted more than 40,000 evacuees in Batangas and nearby Cavite provinces who took shelter in nearly 200 evacuation centres. Officials expected the number to swell.

Solidum warned residents from returning to high-risk villages based on perceptions that the eruption was easing. He warned of pyroclastic flows, super-heated material from the volcano that can travel at great speed and incinerate anything in their path.