Air pollution in the Thai capital forced the closure of more than 350 schools on Friday, city authorities said, the highest number in five years.

Bangkok officials 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 shuttered the most schools since 2020.

"Bangkok Metropolitan Administration has closed 352 schools across 31 districts due to air pollution," the authority said in a message shared on its official LINE group.

On Thursday, more than 250 schools in Bangkok were closed due to pollution, as 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.

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

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

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

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

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

In another bid to curb pollution, a government minister said Friday that public transport in Bangkok would be free for a week.

The capital's Skytrain, metro, light rail system and bus services will be free to users from Saturday, transport minister Suriya Juangroongruangkit told reporters.

"We hope this policy will help reduce pollution."

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.

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 of Punjab in November closed schools in smog-hit major cities for two weeks, 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.