Large parts of Thailand are engulfed by a thick cloud of smog with the north of the country and the capital Bangkok particularly affected due to slash-and-burn land clearance in the region.
Medics have called on the population to wear surgical masks outdoors to protect themselves against the ultra-fine dust particles.
The sky above Bangkok appeared milky white on Wednesday despite there being no cloud in sight, with the sun barely able to penetrate the haze. The city's skyscrapers were shrouded in thick smog.
The pollution is mostly due to slash and burn currently under way in large parts of Thailand but also in neighbouring Myanmar, Cambodia and Laos.
The practice usually causes high particulate matter levels between January and March, particularly in northern Thailand. On Tuesday, values exceeded safe levels in 48 provinces, according to media reports.
According to Nitipatana Chierakul, head of the department for respiratory diseases at Bangkok's Siriraj Hospital, the pollution is particularly harmful for children. "To protect children, households need to install air purifiers," he was quoted as saying by the Bangkok Post.
Schools and kindergartens should restrict outdoor activities, he added.
Meteorologists warned that the smog would persist at least until Thursday, when air quality could start to improve again due to strong winds.
