Air pollution has reached hazardous levels in the Indian capital, Delhi, after many firecrackers were set off to celebrate the festival of Diwali at the weekend.
People celebrated the festival on Sunday night with colourful fireworks across the city, but woke up the next morning to find the city covered in a thick grey blanket of smog.
The situation hasn't changed much since then. The Indian Meteorological Department said Wednesday recorded the worst smog and visibility in 17 years.
Levels of tiny particulate matter (known as PM 2.5) that enter deep into the lungs reached as high as 800 micrograms per cubic metre in the past four days, data from the Delhi Pollution Control Committee showed.