Toxic smog forced dozens of flights to Delhi to be cancelled, diverted or delayed as the Indian city recorded its worst levels of air pollution so far this year.

Authorities have already declared a public health emergency and ordered the closure of schools.

But the air quality deteriorated even further on Sunday, forcing the flight cancellations because of poor visibility.

Sensors across the central region recorded an air quality index of well over 900, far higher than the "severe-plus emergency" level of 500.

Roads were almost deserted as large numbers of people stayed home rather than expose themselves to the noxious atmosphere and doctors reported a spike in patients with respiratory problems.

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

Two airlines, Vistara and Spicejet, warned passengers that several flights had been diverted to Mumbai or Amritsar due to “poor visibility” at Indira Gandhi international airport.

The smog is not expected to clear until later in the week, according to the government environment monitoring agency SAFAR, which has blamed the high pollution in Delhi on agricultural crop burning in neighbouring states.

The country's Supreme Court is likely to hear a petition from the environment agency calling on state governments to take tougher action against farmers who contribute to pollution later this week.

Arvind Kejriwal, Delhi’s chief minister, urged the central government to do more to help the city, adding that the capital’s residents were “suffering for no fault of theirs”.

“Pollution has reached unbearable levels across northern India,” he tweeted.

Mr Kejriwal has already announced plans to halve the number of private vehicles on the roads by imposing “odd-even” traffic days from 4 November.

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He has also launched a campaign handing out five million free anti-pollution face masks, describing Delhi as a “gas chamber”.

The failure to control pollution in the region has left many residents wanting to leave the area, according to a survey of 17,000 people carried out by a private consultancy, Local Circles.