New Delhi's primary schools will be closed to protect children from the 20 million-person megacity's poisonous air, officials said on Friday.

Every winter, a lethal grey cloud covers the nation's capital due to a combination of industrial pollutants, car exhaust, and crop stubble burning by farmers. According to monitoring company IQAir, levels of the most hazardous PM2.5 particles, which are so small they may enter the bloodstream, were nearly 25 times higher on Friday than the daily maximum advised by the World Health Organization.

Delhi chief minister Arvind Kejriwal, under fire from residents and political opponents for failing to address the crisis, said primary schools would be closed from Saturday until “the pollution situation improves.”

“No child should suffer in any way,” Kejriwal told reporters.

Delhi is frequently ranked as one of the world’s most polluted cities. On Friday it again topped IQAir’s list of major cities with the worst air quality.

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.