Visibility for motorists was only five metres, and Nok Air flights between Chiang Mai and Mae Hong Son were suspended.
Officials at the Natural Resources and Environment Bureau in Mae Hong Son said dust particles at less than 10 microns in diametre were found at a density of 219 microgrammes/cubic metre in an average 24 hours – a phenomenon that hampers aviation service.
Mae Hong Son weather station chief Charan Techasueb warned motorists to be more cautious due to poor visibility, which was only five metres at 2pm today.
A forestry official said a satellite survey found 17 hot spots in Mae Hong Son and over 200 in neighbouring Myanmar adjacent to Mae Hong Son.
Hot spots contribute to the thick smoke.