Northern Thailand is grappling with increasingly toxic air pollution levels due to persistent forest fires and agricultural burning.

Residents in the country's northern provinces were urged to stay indoors after the country's Pollution Control Department reported unsafe levels of PM2.5 or hazardous inhalable particles plaguing the region on February 13.

Footage shows a toxic haze clouding the province of Phayao, where the PM2.5 was measured at 136 micrograms per cubic metre - far beyond the safe limit of 50.

Smoke from agricultural burning, and a forest fire from nearby Chiang Mai had also drifted towards the province, blanketing it in smog.

Scientists found that the 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.'