Hotel occupancy in former tourist favourite Chiang Mai has plunged amid an air pollution crisis in the city in northern Thailand.

Officials said reservations in April were just 30 per cent of the same period last year when businesses were still recovering from the pandemic.

Tourism chief La-iad Bungsrithon blamed the PM 2.5 air pollution, which has lead to the once-bustling city becoming one of the worst in the world, regularly ranking below Delhi, Calcutta, Iraq and Bangladesh.

Military officials on Friday, March 29, seen in the video, identified 272 'hotspots' of illegal agricultural burning in the region - marking the highest number in a year.

The majority of these hotspots were found in Samoeng district with 84 spots, followed by Chiang Dao with 42, Mae Chaem with 34, Om Koi with 20, Mae Taeng with 18, Hot with 16, and the remaining spots spread out across 11 other districts.

Kritsayam Kongsatree, director of the Protected Areas Regional Office 16, said that illegal burning has been detected in several forests and national pars.

He said: 'The perpetrators lit fires in the middle of deep forests at several locations, and the reasons behind these actions are unknown, making it challenging for authorities to reach and extinguish them.'

Officials said that more than 200 ground staff were coordinating with aerial support to battle the fires.

Kritsayam said they needed to control the situation urgently as the winds were blowing the smoke from Samoeng district to the Mueang Chiang Mai area, which is a heavily populated economic district.

The smoke obscured visibility, with Doi Suthep becoming barely visible, and many people experienced irritation to their eyes, throat, and noses when outdoors.

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.