The Philippine seismological agency called Thursday for the evacuation of thousands of people near a volcano south of Manila after an eruption sent steam and rock fragments hundreds of metres into the sky.
Taal volcano, which sits in a picturesque lake, has been belching sulphur dioxide for several days, creating a thick haze over the capital and several surrounding provinces, and prompting health warnings.
The last eruption in January 2020 shot ash 15 kilometres (nine miles) high and spewed red-hot lava, crushing scores of homes, killing livestock and sending over 135,000 people into shelters.
Taal burst to life again Thursday afternoon with a "short-lived dark phreatomagmatic plume" that rose a kilometre into the air, the Philippine Institute of Volcanology and Seismology said in a statement.
'We're just raising the alert because something is happening'
The agency warned of possible "succeeding eruptions" as it raised the alert level from two to three, and recommended the evacuation of the volcano island and "high-risk" areas of Agoncillo and Laurel towns.
"We're just raising the alert because something is happening and it can lead to a higher activity," Renato Solidum, head of the agency, told AFP.
Mariton Bornas, head of the agency's volcano monitoring division, said so far they "don't expect the same scenario" as last year's eruption.
A spokesman for the national disaster agency said its local agents had called an emergency meeting with government officials and emergency services. He estimated nearly 15,000 people lived in the most vulnerable areas.
Agoncillo disaster officer Junfrance De Villa told AFP preparations were underway in case residents needed to be evacuated from the lakeside community.
"Some have already taken shelter with relatives," De Villa said.
Pacific 'Ring of Fire'
Taal is one of the most active volcanoes in a nation hit periodically by eruptions and earthquakes due to its location on the Pacific "Ring of Fire" -- a zone of intense seismic activity.
Access to the volcano island, which was once home to a community of thousands, has been prohibited since last year.
Taal shot a column of ash and steam
In January last year, Taal shot a column of ash and steam as high as 15 km into the sky, which forced more than 100,000 people to abandon their homes, widespread flight cancellations and heavy ash falls in Manila.
While the situation could go either way, authorities on Thursday warned that the type of eruption could potentially be more hazardous than that of last year.
Water in Taal's crater boiled before and after its eruption, a video posted on the Facebook page of the seismology agency showed.
Magma made contact with the crater's water, which then turned into gas and vapour, known as a phreatomagmatic eruption.
Eruption and volcanic tsunami
The towns of Agoncillo and Laurel, situated on the lake surrounding the Taal volcano, were in danger from eruption and volcanic tsunami, the seismology agency said.
The national disaster bureau warned of eruption-related quakes.
The evacuation of Agoncillo started late afternoon, Batangas provincial governor Hermilando Mandanas said, with 3,523 families or 14,495 people to be moved to safe areas.
The alert for the Taal volcano, about 70 km (45 miles) south of central Manila, moved to level 3 from level 2 on the 5-level scale, which the seismology and volcanology agency said meant a "magmatic intrusion" at the main crater "could further drive succeeding eruptions".
Authorities in the Philippines started evacuating thousands of people on Thursday after the alert status was raised on a restive volcano that spewed a one-kilometre (0.62 mile) high plume of gas and steam.