Dense fog and hazardous air pollution blanketed northern India and disrupted hundreds of flights on Monday, as harsh winter weather sent temperatures plunging to near-record lows.
New Delhi and surrounding parts of the country are regularly shrouded by haze that hits each winter due to build-up of vehicle fumes, industrial emissions and smoke from agricultural fires.
But thick cloud cover caused by the current cold snap has reduced visibility even further, with authorities blaming the weather for delaying more than 500 flights at the capital's airport.
Six people were killed in the nearby city of Noida when their car veered off the road in the fog and crashed into a canal.
India's weather bureau said Delhi was on course to record its coldest December day since 1901, with a minimum temperature of 2.6 degrees Celsius (35.6 Fahrenheit) early Monday.
In the northeastern state of Assam, zoo authorities put heaters in enclosures to protect tigers from the bracing conditions.
"The animals are not used to this and we are taking special measures to keep the animals, particularly the old ones, warm," Tejas Mariswamy of Assam zoo told AFP.