Bangkok was the only city blanketed by red-coded (seriously hazardous) levels of fine dust pollution among 63 provinces battling thick smog late Thursday morning.

The Geo-Informatics and Space Technology Development Agency reported at 10am that the level of PM2.5 in the capital was at 77.5 microgrammes per cubic metre (µg/m³) of air over the past 24 hours.

The government-set safe threshold is 37.5µg/m³, with red levels indicating a serious health hazard at 75.2µg/m³ and above.

Orange (initially unsafe) levels of PM2.5 were detected in 62 other provinces. Readings ranged from 38.4 to 72.6µg/m³. Most of the provinces were in the Central Plains and the Northeast.

Previously shrouded with red-coded levels, the northern provinces of Chiang Mai, Chiang Rai, and Mae Hong Son saw a shift to orange on Thursday morning, ranging from 41 to 44µg/m³.

Only the South reported safe levels of PM2.5.