Shocking levels of air pollution as northern Thailand is ranked world's worst for fourth straight day

Shocking footage from northern Thailand this morning shows a thick blanket of smog as the region was ranked the worst in the world for air pollution for a fourth consecutive day.

The debilitating toxic smog in backpacker's favourite Chiang Mai saw harmful PM2.5 particle levels rise to 265 micrograms per cubic meter - past Bangladesh, Beijing, Mongolia and India.

Killer air pollution has been caused by farmers burning off their waste crops combined with unseasonably humid, dry weather with little wind.

The levels prompted Chiang Mai University to cancel classes for Wednesday and Thursday, while regional carrier Bangkok Airways to suspend some flights to the city.

Military officials that run the country's government said they were ''monitoring'' the situation and urged locals not to burn rubbish and farmers not to burn their crops.

Pralong Damrongthai, director-general of the Pollution Control Department said: ''Prime Minister Prayut will take a field trip to Chiang Rai with the purpose of following up on measures to deal with the haze in the North.''

Last month, Bangkok was worst hit but the smog appears to have spread north across the country. The air quality index at noon today (March 14) was logged at approximately 270.

Such a level is considered harmful to health and medics and academics have made repeated warnings that it could lead to deadly illnesses. Residents and their pets have previously been seen coughing up blood.

The World Health Organisation caps the acceptable level of PM2.5 particles in the air at 50 micrograms per cubic metre.