Thai authorities deployed cloud seeding planes to try and tackle air pollution as farmers continue to burn watse crops from fields in Thailand.

The Department of Royal Rainmaking and Agricultural Aviation dispatched two CASA planes to Chiang Mai, Lampang, and Phrae provinces as PM2.5 levels remain high.

The department said it will be monitoring haze and smog in northern provinces, and will send cloud seeding planes accordingly.

Thailand has been grappling with severe air pollution for weeks as farmers engage in slash-and-burn agriculture, which triggers forest fires and creates more smoke.

Swiss air quality technology company IQAir reported today that Chiang Mai had an air quality index (AQI) of 181 or 'unhealthy' - ranking second in the world after Karachi in Pakistan, with an AQI of 186.

Thirty-eight new hotspots were also found in Chiang Mai today, bringing the total to 3,582 since January.

Scientists found that the smog in Thailand is at its worst when farmers burn waste crops to cheaply clear their land between late October and April. This is combined with high numbers of polluting cars on the road and large construction projects across the capital.

The seasonal lack of wind and rain, combined with a winter low-pressure system in which cold air is trapped closer to the ground by warm air above – prevent the pollution from being dispersed naturally.

The Thai government has been criticised for failing to tackle the country's air pollution crisis, with bizarre measures such as spraying water into the air and giant purifiers having no impact.