Air quality in Chiang Mai province was measured at 153 on the US AQI listing on Saturday, being ranked as having the world’s 8th worst air quality, as forest fires rage and 150 hotspots were detected, according to the Pollution Control Department.

The most polluted city on Saturday, according to the US AQI, was Calcutta, with air quality being measured at 215, followed by Dhaka in Bangladesh (196), Lahore in Pakistan (184), Kathmandu in Nepal (180), Yangon (174), Bishkek in Kyrgyzstan (157), Krakow in Poland (154) and Chiang Mai (153).

The average level of PM2.5 across the entire province of Chiang Mai was 58.6µg/m³ on Saturday, which exceeds the safe threshold 37.5µg/m³.

Mae Chaem district recorded the most hotspots (48), followed by 27 in Hot district, 24 in Mae Wang, 19 in Chom Thong, 12 in Doi Tao, 3 in Chai Prakan, Omkoi, Mae Taeng and Galyani Vadhana, two in Phrao and Hang Dong, one in Samoeng and Mae Rim.

The worst forest fires were reported in Mae Chaem, where they have been raging uncontrollably across vast tracts of the mountainous areas throughout the night and into the day.

Villagers have blamed the fires on a mistake by officials responsible for forest fuel management, when they burned the fuel without building fire breaks as a precautionary measure first, allowing the fires to spread rapidly.

More firefighters have been mobilised to help control the forest fires.