The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has raised the alert level from 3 to 4 amid the ongoing unrest at the Taal Volcano.
PHIVOLCS also said that a volcanic tsunami could occur and people in nearby areas should be evacuated.
Earlier, the Manila Airport's manager said that flights were temporarily suspended from the airport after the Taal Volcano spewed ash. Arriving flights were also put on hold, the manager added.
Evacuations are underway in towns of San Nicolas, Balete and Talisa in the province of Batangas, which have a combined population of more than 90,000 people.
The Taal Volcano, which is a popular tourist spot, started spewing ash early on Sunday. The Philippine Institute of Volcanology and Seismology said that the volcano has manifested "increased steaming activity in at least five spots inside the main crater”.
Local residents have been sharing photos and videos of the volcano unrest on social media.
The Philippines is situated in the seismic area known as the Ring of Fire which encircles the Pacific Ocean.