Firefighting helicopters doused forest fires that are causing are quality to drop in northern Thailand.

Footage shows the aircrafts sent by the country's Department of Disaster Prevention and Mitigation scooping up water to dump over smouldering woodlands in Chiang Mai province on February 13.

Officials have been struggling to extinguish the forest blaze, which erupted on February 9 at the Ob Luang National Park.

The helicopters had been deployed since the steep, mountainous terrain posed difficulties for firefighters on foot.

The wildfire and agricultural burning done by farmers to clear fields are exacerbating the air pollution in Thailand's northern region.

The Pollution Control Department reported that a large swathe of the country's north, including Chiang Mai province, is experiencing unsafe levels of PM2.5 or hazardous inhalable particles.

Scientists found that smog is at its worst in the country 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.

Data scientist engineer Worasom Kundhikanjana said: 'PM 2.5 pollution has a seasonal trend in Bangkok and the northern provinces, but has only recently received public attention. During this winter haze, the harmful particle pollution level is high throughout the day, including on weekends.

'Unfortunately, spraying water into the air does not appear to be effective, since the volume of water is minuscule compared to actual rain.

'With the start of the monsoon season, the weather in Bangkok will get better, and public attention on this issue will likely fade. However, without immediate policy measures, the problem will come back again next winter.'