The air quality in the northern province of Chiang Mai on Friday was not yet improved from the haze besieging the province and some other northern provinces for the past week, Thai News Agency reported.

Haze from forest and farmland burning off fires still blanket the city of Chiang Mai and the poor visibility is not improving. The particulate level remains higher than the safety standard of 120 micrograms per cubic metre, putting residents at risk from respiratory ailments.

Air quality monitoring station at the Chiang Mai government centre shows the dust particle density levels listed registered at 174 micrograms per cubic metre for particles smaller than 10 microns.

Visibility at Chotana road in the Chiang Mai city centre declined to 300-500 metres because a new round of high pressure cold weather blocked smoke and smog from rising naturally into the atmosphere.

Chiang Mai has been enveloped in haze for a week, causing sickness among local residents. Respiratory ailments among residents was recorded at 40 percent higher than normal.

Environmental authorities blamed crop burning and forest fire as the major cause of the haze problem in the northern region.

The Rain Making Operation Centre for Thailands' upper northern region was not successful in making artificial rainfall to carry dust particles out of the air but rain making flights were continued, to raise humidity in the air until it becomes suitable for rain making.

Many northern provinces of Thailand were hit by forest fire, seasonal forest and farmland fires, since last week. The fire has led to haze problems, causing trouble to residents in the north. The authorities have not yet successfully controlled the fire.