MANILA -- The state weather bureau of the Philippines on Monday warned of a scorching heat index of up to 51 degrees Celsius in at least nine areas across the country.

The state bureau said nine areas in the Philippines are classified as "danger," indicating temperatures ranging from 42 to 51 degrees Celsius.

The rest of the Southeast Asian country is under "extreme caution," with temperatures ranging from 33 to 41 degrees Celsius.

The heat index measures how hot it feels when the relative humidity at a given location is considered. Areas experiencing a danger level heat index will likely experience heat cramps and exhaustion.

"Heat stroke is also possible with continued exposure," the bureau warned.

To avoid potential complications from the extreme heat, the bureau advised the public to limit outdoor activities and drink plenty of water.

The government has allowed schools to conduct online rather than face-to-face classes to protect students, especially children, from high heat index.