A hapless bird was grounded as toxic smog shrouded northern Thailand.

Video shows the black avian walking around dazed in the Mueang Chiang Mai District of Chiang Mai province on March 28.

A portable PM2.5 monitor carried by a local showed that the fine dust level at the time was at around 240 micrograms per cubic metre - far above Thailand's safe threshold of 50.

Chiang Mai this week has ranked the worst in the world for air quality, Swiss air quality company IQAir reported.

Chiang Mai and Chiang Rai - two of the country's most popular city destinations - have been enveloped in a toxic haze for several months, with business owners and residents now urging the local government to declare the district a 'disaster area'.

The designation would allow resources to be mobilised quickly to address the hazardous PM2.5 dust levels, which have been responsible for thousands of hospital admissions.

However, defiant Chiang Rai governor Puttipong Sirimat and Interior Minister Anupong Paochinda refused to address the 'disaster zone' issue, fearing the 'negative impact' of the label on tourism.

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.'