Female boxers at the World Championships in Delhi have been forced to wear surgical masks, scarves or even t-shirts to cover their mouths during training as pollution levels have soared to several times above safe limits.

The boxers, who have gathered in the capital for the AIBA Women’s World Boxing Championships, have said they have not been given protective gear, while the weather, with no wind to blow the smog away, has aggravated the problem in one of the world’s most polluted cities.

On Tuesday, the level of deadly particulate matter PM 2.5, which lodges deep in the lungs, was at 407 micrograms per cubic metre, about eight times the safe limit, according to a reading by the country’s pollution control board.

Last week readings reached 999 micrograms per cubic metre.

In Delhi, high levels of pollution are exacerbated every November and December by the seasonal burning of crop stubble in the neighbouring states of Punjab and Haryana.

Rubbish burning, dust from construction sites and huge diesel emissions from vehicles and industry have also contributed to the problem.

(Reuters (Reuters)

Though the championship is taking place in an indoor arena, teams are worried about the impact of the high level of pollution on athletes.

French coach Anthony Veniant said he had asked for the tournament to be moved out of Delhi but his request was turned down.

“We feel the air is no good. Some of the parents of these players are worried and we tell our players to restrict their time outside,” Veniant said.

New Delhi toxic smog pushes air pollution to peak levels Show all 14 1 /14 New Delhi toxic smog pushes air pollution to peak levels New Delhi toxic smog pushes air pollution to peak levels India's Rashtrapati Bhawan is partly visible due to smog as traffic plies on Rajapth. Smog levels spike during winter in Delhi, when air quality often eclipses the World Health Organization's safe levels AP New Delhi toxic smog pushes air pollution to peak levels Cooler air traps pollutants -- such as from vehicles, building sites and farmers burning crops in regions outside the Indian capital -- close to the ground AP New Delhi toxic smog pushes air pollution to peak levels A man wearing a protective mask walks amidst smog in the early morning in New Delhi Reuters New Delhi toxic smog pushes air pollution to peak levels Indian people receive treatment for respiratory problems at a hospital in New Delhi AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Buildings shrouded in smog Reuters New Delhi toxic smog pushes air pollution to peak levels A combination of pictures showing people wearing face masks to protect themselves against air pollution AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Indian workers are seen in the morning smog as they clean a lane littered with remains of firecrackers AP New Delhi toxic smog pushes air pollution to peak levels Smog envelopes the horizon in New Delhi AP New Delhi toxic smog pushes air pollution to peak levels Motorists on a busy road amid heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels A man cycles past a government building amid heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels Commuters are seen amid heavy smog in New Delhi AFP/Getty New Delhi toxic smog pushes air pollution to peak levels An Indian shepherd walks along his herd of sheep amidst heavy smog AFP/Getty New Delhi toxic smog pushes air pollution to peak levels A train moves through heavy smog EPA New Delhi toxic smog pushes air pollution to peak levels A pedestrian crosses a road near the Indian President's house AFP/Getty

Jay Kowli, secretary general of the Boxing Federation of India, said the air quality was being monitored but ruled out any change of location.

India Gate sits under a thick layer of pollution haze the morning after Diwali festival in Delhi (AP)

“Shifting the venue is impossible. Delhi has the best sports facilities in the country,” Mr Kowli said.

Competitors have been hard at training this week, despite concerns.

“My family is worried. We know it is not good for our body,” said 27-year old Bulgarian Stanimira Petrova, a gold-medallist in the bantamweight category in the championships in 2014.

“It’s difficult. I wear a scarf but I have to get accustomed.”

Daniel Nash, the coach for the Swedish team, said pollution was a problem, but he had asked the boxers to focus on the competition.

“I’m telling my players to not let this issue affect their game,” he said.

Prolonged exposure to high levels of PM 2.5 and PM 10, another pollutant, leads to respiratory illnesses.

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British studies have previously recorded a 7 per cent increase in mortality with each 5 micrograms per cubic metre increase in PM 2.5.