All primary schools have been closed in New Delhi as worsening air pollution in northern India has disrupted flights and obscured the nearby Taj Mahal.
Air quality in northern India has deteriorated over the past week, with New Delhi rolling out measures on Friday that included banning non-essential building work and spraying water over roads.
New Delhi currently has a “severe” air quality level of 424, according to live rankings kept by Swiss group IQAir - the worst among global capitals.
Patients - particularly children - have reportedly been flooding hospitals amid an increase in allergies, acute asthma attacks and coughs while visibility fell to 300m (980ft) at the city's international airport, which diverted flights in zero visibility on Wednesday.
The city battles smog - a toxic mix of smoke and fog - every winter as cold air traps dust, emissions, and smoke from illegal farm fires.
Officials blamed the recent spike in smog on high pollution, combined with humidity, becalmed winds and a drop in temperature.
Toxic smog has obscured India's famed monument to love, the Taj Mahal, about 220km (136 miles) from New Delhi, as well as Sikhism's holiest shrine, the Golden Temple in Amritsar.
India's government on Friday banned non-essential construction in New Delhi, and urged residents to avoid burning coal for heating, to combat the worsening air quality.
The new measures, which include sprinkling water with dust suppressants on roads, as well as mechanised sweeping that would help settle dust, were due to come into effect from Friday morning.
Delhi's Chief Minister Atishi, who uses only one name, also directed all primary schools to shift to online classes.
The government announced the measures on Thursday, but did not say how long they would be in place.
Around 38 per cent of the pollution in New Delhi this year has reportedly been caused by stubble burning - a practice where stubble left after harvesting rice is burnt to clear fields - in the neighbouring states of Punjab and Haryana.
Delhi flights faced delays, with tracking website Flightradar24 showing 88 per cent of departures and 54 per cent of arrivals were delayed as of Thursday afternoon due to smog.
There has reportedly been an increase in residents, particularly children, attending hospital with respiratory issues.
Sahab Ram, a paediatrician in Punjab's Fazilka region, told news agency ANI: “There has been a sudden increase in children with allergies, cough and cold ... and a rise in acute asthma attacks.”
Delhi's minimum temperature fell to 16.1C (61F) on Thursday from 17C (63F) the previous day, weather officials said.
Pollution in New Delhi was likely to stay in the "severe" category on Friday, the earth sciences ministry said, before improving to "very poor", or an index score of 300 to 400.
The number of farm fires to clear fields in northern India has risen steadily this week to almost 2,300 on Wednesday from 1,200 on Monday, the ministry's website showed.
Lahore, the capital of Pakistan's eastern province of Punjab, was rated the world's most polluted city on Thursday, in IQAir's rankings. Authorities there have also battled hazardous air this month.
