The Mae Hong Son operation centre for tackling forest fires and smog added that the PM2.5 level in Muang district was measured at 196 µg/m3 and at 132 µg/m3 in Mae Saring district.
The safe threshold of PM2.5 (particulate matter smaller than 2.5 microns in diameter) is 50 µg/m3.
Pai town is the heart of Pai district, which is the northeastern border district of Mae Hong Son.
The centre said on Thursday that satellite photos showed 313 forest fire spots in the northern province at the end of Wednesday.
It said 190 forest fires were spotted by satellite on Thursday morning and the number is expected to rise during the day. There were 75 forest fire spots in Pai district, 50 in Muang, 24 in Khun Yuam, 13 in Pang Ma Pha, 13 in Mae Sarian, 8 in Sob Moei, and 7 in Mae La Noi district.
Arkhom Boonnonetae, chief of the Salawin wildlife sanctuary in Mae Hong Son, said on Thursday that he had dispatched officials to talk to villagers in Tambon Sao Hin of Mae Sariang district to ask them to refrain from burning weeds and harvest leftovers.
Meanwhile, Muang district chief Sangkhom Kudchiangsaen said he had dispatched officials to combat forest fires behind a petrol station and behind the Thanyarak Hospital on Thursday.
Also on Thursday, Anek Panthayom, director of the Pai operation centre to fight forest fires, said his centre had coordinated with the local administration to spray water in Pai town to try to lower PM2.5 in the air.
The centre also dispatched officials to try to contain forest fires in Ban Sobsa village in Tambon Muang Paeng, which is next to Kalayaniwattana district, Anek added.