Thick smoke cloaked northern Thailand as rampant farm burning continues in the region.

Footage shows a heavy grey haze shrouding Chiang Rai province on Wednesday morning March 27.

The Pollution Control Department said PM2.5 air pollution in the Mae Sai district reached 209 microgrammes per cubic metre - more than 40 times the safe level set by the World Health Organisation of five microgrammes.

Officials said the smog reduced visibility to one kilometre. Residents had also reported stinging in their eyes and noses.

Chiang Rai governor Puttipong Sirimat said he had last month banned agricultural burning in the province. However, air pollution was still prevalent due to farmers ignoring the rule as well as fire in neighbouring countries, including Myanmar, Cambodia, and Laos.

Dangerous levels of deadly PM 2.5 particles - which cause cancer and other debilitating illnesses - are recorded every year in Thailand between December and April when farmers across Southeast Asia burn waste crops to clear their land.

The rudimentary method, known as 'slash and burn', is quicker and cheaper than modern machinery, leaving relatively poor landowners unwilling to heed environmental and health concerns over economic necessity.

Despite paying lip service for several years, politicians have failed to stop individuals from burning their land due to it being cheaper and easier than modern farming methods.

In March 2023, the Public Health Ministry of Thailand reported that around 1.3 million people in the country had been unwell due to the rising levels of air pollution. Officials said 200,000 residents were hospitalised in a single week.

Researchers from Peking University in Beijing, China, found that exposure to PM 2.5 air pollution is associated with an increased risk of lung cancer.

In December, Dr Krittai Thanasombatkul from Chiang Mai - one of the world's worst cities for air pollution - died of lung cancer. He had previously blamed PM 2.5 microdust particles for his condition.

The New York State Department of Health says PM 2.5 also increases the risk of heart disease, asthma, and low birth weight.

Medics from South Korea published research in the National Institute of Health in the United States that said the pollutant increases the risk of stroke, ischemic heart disease, chronic obstructive pulmonary disease (COPD), lung cancer, and other illnesses such as immune deficiency and even obesity.