The state volcanology and seismology institute said it observed upwelling of hot volcanic fluids in the Taal volcano's crater lake, resulting in the emission of volcanic gases.
The alert remained at level 1 on a five-level scale, denoting a "slight increase in volcanic earthquake, and steam or gas activity".
"We have reports of respiratory illnesses in Batangas province due to intoxication from the volcanic smog," Randy Dela Paz, operations section chief at the civil defence's southern Manila office, told DWPM radio.
Volcanic smog, or vog, consists of fine droplets containing volcanic gas like sulfur that can cause irritation of the eyes, throat and respiratory tract.
Authorities suspended Friday classes in dozens of towns and cities Cavite, Laguna, and Batangas provinces adjacent to Taal volcano, and in five cities in the capital region.
Persons:
Randy Dela Paz, Neil Jerome Morales, Michael Perry
Organizations:
Manila spewed, Thomson
Locations:
MANILA, Philippine, Manila, Batangas, Philippines, Cavite, Laguna, Taal