Alarming levels of air pollution led to the closure of more than 250 schools in Bangkok today, local authorities said, as they appealed to the Thai capital’s millions of residents to work remotely.

From kindergartens to high schools, about 194 schools out of 437 run by the Bangkok Metropolitan Administration remained closed today, they said. This is the largest number of school closures since 2020, when at the height of pollution all schools run by the Bangkok authorities were closed.

58 schools out of 156 under the Bureau of Elementary Education, a central government body, were also closed today, according to authorities.

Bangkok, which woke up under a haze of noxious gases, was today the world’s sixth most polluted city, according to Swiss company IQAir.

The concentration of PM2.5 microparticles, which are the most dangerous as they disperse directly into the bloodwas surpassing this morning the eightfold of permissible limit set by the World Health Organization (WHO).

Authorities have also asked residents to work from home, but the telecommuting system developed by Bangkok’s metropolitan authorities for peak pollution cases brings together only 100,000 workers in a city of about 10 million people.

Authorities also restricted truck access to six road arteries in some areas of the capital until the end of Friday.

Air pollution peaks at this time of year in Thailand, as in many countries in the region, due to cold, stagnant air that cannot adequately remove vehicle emissions and smoke from agricultural burning.