The warning was issued on Sunday after the office of natural resources and environment of Mae Hong Son found the level of harmful dust particles (PM10) was measured at 242 microgrammes per cubic metre. The standard level is 120 microgrammes per cubic metre.
Saturday's level of harmful dust particles was measured at 324 microgrammes per cubic metre.
Dr Tossathep said the condition of people sufferring from respiratory problems, asthma, allergies and inflammation of the lungs could get worse from inhaling the harmful dust particles.
These people as well as the elderly and children should stay in their houses and refrain from outdoor exercise. If it is necessary to leave the house, they should wear protective masks, he said.