Authorities in Delhi have announced that schools are to close for a week as the Indian capital’s pollution control body warned of a looming health emergency due to smog. Delhi is ranked one of the world’s most-polluted cities, with a hazardous mix of factory and vehicle emissions and smoke from agricultural fires turning its air a toxic grey every winter. On Saturday, levels of PM 2.5 particles – the smallest and most harmful, which can enter the bloodstream – topped 300 on the air quality index. That is 20 times the maximum daily limit recommended by the World Health Organization. “Starting Monday, schools are being shut so that children don’t have to breathe polluted air,” Delhi’s chief minister, Arvind Kejriwal, told reporters in the city of 20 million people. Kejriwal said no construction activity would be allowed for four days, starting on Sunday, to cut down dust from vast open sites. Government offices were asked to operate from home and private businesses advised to stick to work-from-home options as much as possible. The central pollution control board on Friday told residents to “limit outdoor activities and minimise their exposure” and advised government authorities to prepare “for implementation of measures under ‘emergency’ category”. It said the poor air quality would probably last until at least Thursday [18 November] due to “low winds with calm conditions during the night”. Hospitals were reporting a sharp rise in patients complaining of breathing difficulties, the Times of India reported. “We are getting 12 to 14 patients daily in the emergency, mostly at night, when the symptoms cause disturbed sleep and panic,” Dr Suranjit Chatterjee from Apollo Hospitals told the newspaper. Earlier on Saturday, the supreme court suggested imposing a pollution lockdown on Delhi to help with the air quality crisis. “How will we live otherwise?” India’s chief justice, NV Ramana, said. Delhi’s government has been vowing for years to clean up the city’s air. The burning of agricultural waste in neighbouring states – a major contributor to the city’s pollution levels every winter – has continued despite a supreme court ban. Tens of thousands of farmers around the capital burn their stubble – or crop residue – at the start of every winter, clearing fields from recently harvested paddies to make way for wheat. The number of farm fires this season has been the highest in the past four years, according to government data. Earlier this year, the Delhi government opened its first “smog tower” containing 40 giant fans that pump 1,000m3 of air a second through filters. The $2m installation halves the amount of harmful particulates in the air but only within a radius of one square kilometre (0.4 square miles), according to engineers. A 2020 report by the Swiss organisation IQAir found that 22 of the world’s 30 most polluted cities were in India, with Delhi ranked the most polluted capital globally. The same year, the Lancet said 1.67 million deaths were attributable to air pollution in India in 2019, including almost 17,500 in the capital. In recent days the river flowing through Delhi, the Yamuna, has also been choked with sickly white foam. The city government has blamed the blight on “heavy sewage and industrial waste” discharged into the river from farther upstream.