The alert for the Taal volcano, about 70 km (45 miles) south of central Manila, was raised to level 3 from level 2 which "means that there is magmatic intrusion at the main crater that may further drive succeeding eruptions," the seismology and volcanology agency said.
Taal spewed clouds of ash in January last year, prompting the evacuation of more than 100,000 people.