A small but active volcano on the main Philippine island of Luzon continued to belch massive columns of ash, steam and lava yesterday, shutting down the capital Manila and setting off massive evacuations in provinces near it.
Government seismologists warned that a "hazardous, explosive eruption" could occur at the Taal volcano - perhaps within days - either at the main crater or new vents that were observed yesterday.
"So now, the eruption is not only seen inside the crater, but along the side of the volcano as well," Mr Renato Solidum, head of the state-run Philippine Institute of Volcanology and Seismology (Phivolcs), told reporters.
The agency raised the volcano alert level to four - out of a maximum of five - which suggests that a violent eruption could be imminent. It could not say when the crisis would pass.
"It could last for at least three days, as in 1911, or as long as seven months, as what happened in 1754," said Ms Mariton Bornas, who is in charge of monitoring volcanoes at Phivolcs.
The Taal volcano, about 65km south of Manila, rumbled back to life on Sunday, blasting steam, ash and pebbles up to 15km into the sky.
The ashfall reached as far as Manila, covering dozens of towns and cities, including the main business district of Makati City. A change of wind direction means ash is blowing over municipalities not included in earlier emergency plans, swelling the number of communities affected, Bloomberg reported.
Yesterday, schools and government offices were closed. The stock exchange suspended trading and many private businesses shut for the day too. Schools and government offices will remain closed today as well.
Streets that would normally be snarled with some of the world's worst traffic were largely empty, as most of the city's population of some 13 million opted to stay home.
Those who had to go out wore dust masks or handkerchiefs across their faces. The country's largest pharmacy chain announced that it had run out of dust masks, as health officials warned that the ash could cause respiratory problems.
Flight operations at Manila's international airport partially resumed, after at least 240 flights were delayed or cancelled on Sunday.
One flight that did land carried President Rodrigo Duterte, who was returning from his home city of Davao in the southern Philippines. He had been unable to fly on Sunday because visibility was low.
Singapore's Ministry of Foreign Affairs advised those intending to travel to affected areas to defer their travel. Singaporeans already in the Philippines have been asked to heed instructions of the local authorities.
At least 10 flights between Singapore and Manila were cancelled or rescheduled yesterday, according to Changi Airport's website. These included flights operated by Singapore Airlines, Scoot, Jetstar Airways and Philippine Airlines.
Aircraft are still advised to avoid the airspace around the volcano as ash and ballistic fragments pose risks.
Meanwhile, tens of thousands of people were evacuated in provinces near Taal. The National Disaster Risk Reduction and Management Council said more than 25,000 had been taken to 75 evacuation centres. More were expected to be evacuated.
The 14km danger zone declared around Taal covers a population of some 460,000.
One of the most active volcanoes in the Philippines, Taal has erupted more than 30 times in the past 500 years, most recently in 1977.