Bangkok officials also announced free public transport for a week in a bid to reduce traffic in a city notorious for noxious exhaust fumes.

Seasonal air pollution has long afflicted Thailand, like many countries in the region, but this week's hazy conditions have closed the most schools since 2020.

"It's hard to breathe... I really feel the burn in my throat," drinks seller Benjawan Suknae, 61, told AFP.

"I think (school closures) could help to a certain point."

The Bangkok Metropolitan Administration said it had closed 352 schools across 31 districts due to air pollution.

More than 250 schools in Bangkok were closed on Thursday, and officials urged people to work from home and restricted heavy vehicles in the city.

Air pollution hits the Southeast Asian nation seasonally as colder, stagnant winter air combines with smoke from crop stubble burning and car fumes.

The level of PM2.5 pollutants -- cancer-causing microparticles small enough to enter the bloodstream through the lungs -- hit 108 micrograms per cubic metre by Friday, according to IQAir.

The World Health Organization (WHO) recommends 24-hour average exposures should not be more than 15 for most days of the year.

The reading makes the Thai capital currently the world's seventh-most polluted major city.

By Friday morning, 352 of the 437 schools under the Bangkok Metropolitan Authority (BMA) had shut their doors, affecting thousands of students.

Interior Minister Anutin Charnvirakul ordered a ban on Thursday on stubble burning -- intentionally burning leftover crops to clear fields -- with those responsible risking legal prosecution.

In another bid to curb pollution, the capital's Skytrain, metro, light rail system and bus services will be free to users for a week from Saturday, transport minister Suriya Juangroongruangkit told reporters.

"We hope this policy will help reduce pollution," he said.

Prime Minister Paetongtarn Shinawatra, who is currently attending the World Economic Forum in Switzerland, called for tougher measures to tackle pollution on Thursday, including limiting construction in the capital and seeking cooperation from nearby countries.

The city's authorities introduced a voluntary work-from-home scheme for three days this week.

"I think there should be more awareness raised (by the BMA) and maybe a work-from-home policy would be best," said freelancer Wisut Kitnarong, 59.

- Regional problem -

Cities in neighbouring Vietnam and Cambodia also ranked high on IQAir's most-polluted list on Friday, with Ho Chi Minh second and Phnom Penh fifth.

Cambodia's environment ministry confirmed on Friday that the air quality in Phnom Penh and three other provinces had reached a "red level", meaning highly polluted.

The ministry said in a statement that the air pollution was caused by climate change, waste incineration and forest fires, and urged the public to monitor their health and avoid outdoor activities.

Air pollution has closed schools across other parts of Asia recently -- specifically Pakistan and India.

Nearly two million students in and around New Delhi were told to stay home in November after authorities ordered schools to shut because of worsening air pollution.

Pakistan's most populated province, Punjab, closed schools in smog-hit major cities for two weeks in November, with thousands hospitalised as air pollutants hit 30 times the level deemed acceptable by the WHO.

Bangkok's school closures come as UNICEF said in a report that 242 million children's schooling was affected by climate shocks in 2024.

Climate change can worsen the problem of air pollution which is considered a "secondary impact of climate-induced hazards", according to the report published Friday.

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