Severe air pollution continues to cloud northern Thailand.

Aerial footage shows the gray mist of harmful PM2.5 particles shrouding buildings in Chiang Mai City on April 10.

Another clip taken from a plane that departed from Chiang Mai airport shows the opaque blanket of pollutants hovering over the city.

The aircraft had to turn on its lights in order to be observed from the ground.

Swiss air quality monitor IQAir rated Chiang Mai as having the worst air quality in the world today, with a rating of 195 and readings of 142 micrograms of PM2.5 particles per cubic metre - around 29 times the safe level recommended by the World Health Organisation (WHO).

Chiang Mai Governor Nirat Pongsitthaworn finally declared several villages in Chiang Mai 'disaster zones' last week. The designation will allow resources to be mobilised quickly to address the hazardous PM2.5 dust levels, which have been responsible for thousands of hospital admissions.

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. It has been worsened in recent years by rising demand for food and powerful agro-business lobbyists that can stifle the government's control over farmers.

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 – hampers the pollution from being dispersed naturally by wind.

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. The air pollution also affects China.