Thousands of schools in the Philippines suspended in-person classes on Friday, the education department said, as parts of the tropical country endured dangerously high temperatures.

Official figures showed 5,288 schools across the archipelago nation switched to remote learning, affecting more than 3.6 million students.

The months of March, April and May are typically the hottest and driest in the archipelago nation, but conditions have been exacerbated by the El Nino weather phenomenon.

Many schools have no air conditioning, leaving students to swelter in poorly ventilated, crowded classrooms.

The Department of Education has issued an advisory giving school heads the power to decide when to switch to remote learning "in cases of extreme heat and other calamities".

Some schools have reduced class hours to avoid teaching during the hottest times of the day.

The heat index was expected to reach the "danger" level of 42 or 43 degrees Celsius in several areas of the country on Friday, the state weather forecaster said.

In Manila, the heat index was forecast to hit the "extreme caution" level of 40C, when heat cramps and exhaustion are possible.

The country's heat index measures what a temperature feels like, taking into account humidity.

Friday's actual maximum temperature in Manila was 35.5C.