The state weather bureau recorded on Tuesday the highest heat index - 51.7 degrees Celsius - so far this year in a northern Philippine city.
The Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) said the heat index recorded at 2 p.m. local time in Dagupan City in Pangasinan province is dangerous, saying it can cause heat cramps and heat exhaustion to people.
"Heat stroke is probable with continued activity," the bureau said.
The heat index is defined by PAGASA as "human discomfort index that gives the 'apparent' temperature or what human perceive or feel like the temperature affecting their body", which is normally higher than actual air temperature.
The bureau advised people to stay indoors as much as possible, if air conditioning is not available, and stay on the lowest floor out of the sunshine."
It further asked people to "wear lightweight and light-colored clothing."
"Drink plenty of water regularly. The body needs water to keep cool. Water is the safest liquid to drink during heat emergencies," the bureau added.
PAGASA also said 13 other areas in the Philippines fell in the "danger" category on Tuesday. Among those with the highest temperatures are Cuyo town in Palawan province of the central Philippines at 46.2 degrees Celsius, and Tuguegarao City in Cagayan province of the northern Philippines at 43.5 degrees Celsius.
A heat index of 42 degrees Celsius was also recorded in the Metro Manila, the country's capital.
The Philippine Department of Health earlier advised the public to keep themselves hydrated and protected from sun exposure.
Several provinces in the Philippines are experiencing dry spell conditions this March till May or June due to El Nino weather phenomenon.