In pictures: Thick toxic haze engulfs Delhi, schools to remain closed

Authorities in the smog-ridden Indian capital New Delhi on Sunday extended an emergency schools closure by a week, with no signs of improvement in the megacity's choking levels of pollution.

"As pollution levels continue to remain high, primary schools in Delhi will stay closed till 10th November," said Delhi Education Minister Atishi Marlena. For Grade 6-12, schools are being given the option of shifting to online classes, she added.

Every autumn New Delhi is blanketed in acrid smog, primarily blamed on stubble-burning by farmers in the neighbouring agrarian states.

The toxic air on Saturday had forced Sri Lanka to cancel their training session. The team was practising for a World Cup clash on Monday against Bangladesh in the heavily-polluted Indian capital.

The city is regularly ranked as one of the most polluted on the planet, with its annual smog blamed for hundreds of thousands of premature deaths each year.

The Indian capital - which has a population of 30 million - once again ranked as the world's most polluted city Sunday, according to monitoring firm IQAir.

The city's air quality index (AQI) on Sunday was 471, putting it in the "hazardous" category. It was followed by Lahore in Pakistan at a "very unhealthy" of 261.

An AQI of 0-50 is considered good, while levels 400-500 impacts healthy people and is dangerous to those with existing diseases.

Delhi state annually imposes restrictions on construction activities and orders some vehicles off roads when pollution reaches severe levels.

But critics say that governments wilfully ignore the agricultural primary source of the public health crisis. The farmers in neighbouring states are a powerful electoral lobby and elected leaders have long resisted calls to impose strict fines and other punitive measures on them for their actions.

Levels of the most dangerous PM2.5 particles - so tiny they can enter the bloodstream - reached 570 micrograms per cubic metre on Sunday according to IQAir, nearly 40 times the daily maximum recommended by the World Health Organization.

A Lancet study in 2020 attributed 1.67 million deaths to air pollution in India during the previous year, including almost 17,500 in the capital.

And the average city resident could die nearly 12 years earlier than expected due to air pollution, according to an August report by the University of Chicago's Energy Policy Institute.

India is heavily reliant on polluting coal for energy generation, resisting calls to phase it out, and its per capita coal emissions have risen 29 percent in the past seven years.