BANGKOK • The haze affecting northern Thailand has reached levels that can be considered harmful to health, according to director-general Chatchai Promlert of the Disaster Prevention and Mitigation Department.

He said on Tuesday that the Pollution Control Department had reported that the levels of dust particles measuring less than 10 micrometres - known as PM10 - had crossed the prescribed safe threshold of 120 in four out of nine provinces where monitoring was conducted. The level of PM10 in the nine regions - Chiang Rai, Chiang Mai, Lampang, Lamphun, Mae Hong Son, Nan, Phrae, Phayao and Tak - was measured at between 68 and 160.

The haze level was considered unhealthy in Chiang Mai, Lampang, Lamphun and Phrae provinces, the Bangkok Post reported.

Mr Chatchai said that he had asked agencies in the North Region to closely monitor the situation and air quality. He advised them to be prepared to spray water to reduce the levels of dust particles if necessary and called for firefighting equipment to be put on standby.

Mr Chatchai also urged people not to burn garbage and agricultural trash, which would exacerbate the situation. He added that people should avoid outdoor activities and wear face masks when outdoors. He also advised people to drive with extra precaution as visibility was compromised.

Thailand's Interior Ministry has instructed all northern and north-eastern provinces to accelerate forest fire and haze mitigation measures, according to Permanent Secretary Krissada Boonyarat.