Chiang Mai Governor Wichai Srikwan yesterday removed the "disaster zone" label as the haze over this northern province has begun to lift.

"We hope to relieve the worry of Chiang Mai residents and boost tourism in the run up to Songkran," Wichai said.

The festival will begin on April 13.

Chiang Mai was declared a disaster zone earlier this month when thick smog engulfed it.

Wichai said he had already written to the Social Development and Human Security Ministry to inform it of his decision.

Wichai said that declaring the province a disaster zone allowed him to assist people financially.

"But so far, we haven't needed to," he said.

The haze problem hit the country's North early this month, affecting the health of people there.

As of yesterday, the situation had returned to normal in all provinces except Mae Hong Son, where dust particles smaller than 10 micrograms (PM10) in the air stood at 150 micrograms per cubic metre.

The normal level requires that PM dust particles are no more than 120 micrograms per cubic metre.

Six aircraft are continuing to carry out royal rainmaking operations every day to clear up the haze, reduce air pollution and to tackle the drought.

According to the Public Health Ministry, the air pollution has increased the number of patients seeking treatment at state-owned medical facilities.

Between March 15 and March 22, 57,765 patients sought treatment in Chiang Mai, Chiang Rai, Kanchanaburi, Lampang, Lamphun, Mae Hong Son, Nan, Phayao, Phrae - or about 7,220 patients a day on average. More than 90 per cent of them had respiratory problems.

"With the situation improving, the number of patients in these provinces has already come down to just 4,605 on Thursday," Public Health Minister Mongkol na Songkhla said.

He added his ministry sent 150,000 masks to Mae Hong Son yesterday to help local people cope with the haze.

 "Normally, our body can discharge dust particles it has inadvertently taken in by sipping warm water often," Mongkol said.