Hazardous pollution levels in northern Thailand have left Chiang Mai choking under thick smog, with local residents worried about the impact on tourism — and their health.

Smoke from forest fires and farmers burning fields has suffocated the tourist city, with the global air monitoring platform IQAir ranking it among the most polluted places in the world.

According to IQAir, Chiang Mai on Wednesday had a PM2.5 dust level of 144.7 microgrammes per cubic metre (μg/m³), down from above 200 earlier this month but still far beyond the World Health Organization’s “safe” limit of 25 μg/m³.

As most of the country prepares to celebrate the Songkran festival the mood in Chiang Mai is glum.

“It made me want to cry,” said Kanchaya Boontan, 40, who runs CM Siam Travel, a tourism firm.

“This year is bad, normally pollution is not too long but the foreigners have seen the news,” she added, adjusting her N95 mask.

The pollution is mainly caused by farmers burning their fields, said the National Astronomical Research Institute of Thailand.

This year alone, nearly 2 million people in Thailand have needed hospital treatment for respiratory conditions caused by air pollution, according to the Ministry of Public Health.

Chiang Mai cardiologist Rungsrit Kanjanavanit told AFP that officials are not doing enough to tackle the pollution, worried about its impact on the country’s vital tourist economy.

The pollution affects children and the elderly the most, Rungsrit said.

Chokchai Mongkolcho, visiting from northeastern Roi Et province, said the smog “hides the city’s beauty”.

“It makes me wonder if I’ll ever come back here again if there’s still pollution like this.”