New Delhi is experiencing its most dangerous levels of air pollution in years, with schools and construction sites being shut down as the Indian authorities discuss emergency measures.
For more than a week, the skies of India's capital have been filled with a thick haze that has made people's eyes sting and their throats sore as the government declares an "emergency situation".
The Centre for Science and Environment, a research and lobbying organisation, said government data shows that the smog that has covered the city for the last week is the worst in 17 years.
Experts have blamed the air pollution on various sources, from diesel-burning cars and seasonal crop burning to garbage fires and stoves fueled with kerosene and cow dung. Winter weather patterns also mean there is less wind to circulate the air.
The smog "remains in the lower atmospheric layer," said Dr Surya Kant Tripathi, who heads the pulmonary medicine department at King George's Medical University in Lucknow.
He urged people to avoid going outdoors, unless wearing face masks. "Higher air pollution levels may take days to settle," he said.
Meanwhile, people have been sharing photos of the thick smog engulfing the city:
The phenomenon has also led to people taking "smog selfies":
In New Delhi the levels of PM2.5 - the tiny particulate matter that can clog lungs - were at least above 400 micrograms per cubic metre on Monday.
That's more than 40 times what's considered safe by the World Health Organisation, and more than six times the limit set by Indian law.
New Delhi has also ordered the temporary closure of a nearby coal-burning power plant, as well as construction and demolition sites blamed for sending huge plumes of fine dust particles into the air.
It also ordered that roads be doused with water to settle dust, and banned diesel-powered electricity generators for 10 days except at hospitals and cellphone towers.
India's Supreme Court will hear a plea demanding that authorities do a better job of monitoring air quality and take more serious steps to cut pollution on Tuesday.