Punjab's Lahore was ranked the most polluted city in the world Wednesday by a Swiss air quality monitor.

By evening the air above the city of 11 million had cleared slightly.

But levels of PM2.5 -- the smallest and most harmful particles polluting the air -- were still at 118 micrograms per cubic metre, nearly eight times the WHO's daily recommended maximum.

"Children are experiencing breathing diseases... for God's sake, find a solution," labourer Muhammad Saeed told AFP.

In recent years, Lahore residents have built their own purifiers and filed lawsuits against government officials in desperate bids to clean the air.

But authorities have been slow to act, blaming the smog on India or claiming the figures are exaggerated.

Lahore is consistently ranked one of the world's worst cities for air pollution.

"We are poor people, we can't even afford a doctor's charges," shopkeeper Ikram Ahmed told AFP.

"We can only plead with them to control the pollution. I am not a literate person, but I have read that Lahore has the worst air quality and then comes India's Delhi. If it continues like this, we will die."

Labourer Saeed said he had stopped taking his children outside for walks because of the dirty air.

"There are factories and small industries operating here -- either shift them somewhere else, give them compensation or provide them with modern technology, so we can get rid of this smog," he said.

India's capital, New Delhi, has shut schools and coal plants as it battles dangerous levels of air pollution in the region that on Wednesday also left Lahore in neighbouring Pakistan choking on acrid smog.

Air quality has worsened across northern India and adjacent parts of Pakistan in recent years, as industrial pollutants, smoke from seasonal crop burn-off, and colder winter temperatures coalesce into toxic smog.

Delhi is consistently ranked the world's worst capital for air quality, with levels of pollutants last week reaching more than 30 times the maximum limit recommended by the World Health Organization.

The city on Tuesday ordered the closure until the end of the month of six of 11 coal-fired power plants surrounding the metropolis in a bid to tackle the filthy air.

The move comes after India led the charge at the weekend to weaken anti-coal pledges at the UN COP26 climate summit, with critics saying it prioritised economic growth over the planet's future.

The Indian capital of 20 million people has also cancelled school classes and urged people to work from home, while banning non-essential trucks from entering the city in an effort to clean the smog.

In an order passed late Tuesday, the city's Commission for Air Quality Management said all education institutions should remain shut until further notice.

"Anti-smog guns" -- which spray mist into the air -- and water sprinklers were ordered to operate at pollution hotspots at least three times a day.

The commission also said that at least half of government workers were being sent home and private firms should follow suit.

The order came days after the Delhi government pushed back against a call by India's Supreme Court to declare the city's first "pollution lockdown", which would restrict the population to their homes.