"The province remains a disaster-hit zone," Mae Hong Son Governor Direk Konkleeb said.

Fine-dust particles are smaller than 10 micrograms or PM10. Yesterday, the area recorded 160 micrograms of fine-dust particles per cubic metre (mpcm) in the air. The acceptable level is 120 mpcm.

The smog crisis hit Mae Hong Son a month ago and from March 1 to March 26, 6,161 local residents sought treatment relating to respiratory problems which could be blamed on the haze.

"If the hazy conditions continue, more patients will show up," the provincial public health chief Dr Suwat Kittidilokkul said.

Direk said forest fires, though not serious, were still raging through some areas.

Apiwat Kunarak, who heads the Environment Office Region 1, said forest fires along the border were contributing to the smog in the North's largest city.

Last Friday, Chiang Mai dropped its "disaster zone" label, when the amount of fine dust particles in the city's air was within acceptable limits. But it has increased since. Yesterday, the amount of fine dust particles in Chiang Mai had reached 132 mpcm.

In Chiang Rai, the amount stood at 157 mpcm and local people continued to flock to hospitals seeking treatment for respiratory problems.