MANILA, April 22 (Xinhua) -- The Philippine state weather bureau PAGASA advised Filipinos on Sunday to stay indoor and hydrated as the country's heat index sizzled to over 41 degrees Celsius in at least 14 areas.

The bureau said the heat index rose past 41 degrees Celsius on Sunday. In Sangley Point in Cavite province, the bureau said heat index rose to a high of 47.7 degrees Centigrade.

The heat index is the measure of the temperature that a person feels, and is essentially the "apparent temperature" felt by the human body, which is computed by factoring in the humidity as well as the ambient dry bulb temperature.

The bureau's scale classifies heat index temperatures from 41 to 54 degrees centigrade as dangerous. It warns that at this level "heat cramps and heat exhaustion are likely" and that "heat stroke is probable with continued activity."

"Stay indoors as much as possible. If air conditioning is not available, stay on the lowest floor out of the sunshine," the bureau said in an advisory.

The bureau also urged Filipinos to wear lightweight and light-colored clothing, adding that light colours will reflect the sun's energy.

"Drink plenty of water regularly. The body needs water to keep cool," it said.

It also said that water is the safest liquid to drink during heat emergencies. "Avoid drinking liquor because it dehydrates the body," it said.

Moreover, the bureau urged Filipinos to eat small meals. "However, eat more often. Avoid eating foods high in protein which can increase metabolic heat," the bureau said.

March to May is the summer months in the Philippines and are classified as hot and dry. June to October is rainy, with the months between July and September characterized by typhoons.

November to February is the coolest months and a good time to visit the Philippines as far as weather is concerned.