Footage shows the chronic air pollution from agricultural burning clouding roads in northern Thailand today.

The toxic haze with deadly levels of PM2.5 particles has engulfed Chiang Mai and neighbouring Chiang Rai province - making them the worst cities in the world for air quality this week.

Hospital data shows that more than 3,500 people were admitted for respiratory issues in Chiang Rai alone. They had sore throats and nasal irritation - symptoms that can lead to killer lung diseases in the long term.

Bungling state officials - powerless in the face of food conglomerates with immense lobbying power - have been unable to control the seasonal crop burning in rural northeast Thailand, Laos, Myanmar and Cambodia where burning is used to quickly clear land to meet rising demand.

Since 2018, the state has used bizarre methods such as giant air purifiers and water hoses - or advising people to stay indoors - without successfully stopping the annual pollution.

Varawuth Silpa-archa, minister of Natural Resources and Environment said the government may now impose temporary measures including a curfew to prevent farmers from burning their fields.

He said: 'We don't want to impose strict measures, but if people do not cooperate then we have to impose harsh rules.'

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.'