The air quality at most monitoring stations was in the "severe" category .
Thirty-two flights were diverted from Delhi airport on Sunday morning due to low visibility caused by a thick smog that enveloped the national capital.
The air quality index (AQI) hit 473 at 9 am, according to Central Pollution Control Board (CPCB) data. The air quality at most monitoring stations was in the 'severe' category. At ITO, the AQI levels were 488, while at Anand Vihar and RK Puram they were 483 and 457.
The Delhi airport operator tweeted that flight operations have been affected and requested passengers to contact airlines for updated flight information.
Passengers are requested to contact the airline concerned for updated flight information. Any inconvenience caused is deeply regretted.
"Due to bad weather, flight operations affected since morning 9 am in T3 airport (Delhi). Twelve flights are diverted to Jaipur, Amritsar and Lucknow," an Air India spokesperson was quoted as saying by PTI.
Chief Minister Arvind Kejriwal tweeted asking the central government to take immediate steps to provide relief. "Pollution has reached unbearable levels across North India. Delhi government has taken many steps. Delhiites have made many sacrifices. Delhi is suffering for no fault of theirs," he tweeted.
The pollution levels had gone below the "emergency" levels on Saturday after rain in some parts of Delhi and an increase in wind speed.
The Supreme Court-mandated Environment Pollution (Prevention and Control) Authority had declared a health emergency in the city on Friday. It has directed measures, including shutting down of schools and a complete ban on construction activities in Delhi and neighbouring towns until November 5.