The national capital experienced the season's first dense fog on Wednesday with the visibility dropping to zero at the Delhi airport.
A few flights were diverted due to the low visibility conditions, an official said.
Zero-metre visibility was recorded at the Indira Gandhi International Airport at 8.30 am with the Runway Visual Range varying between 125 and 500 metres at different locations, the India Meteorological Department (IMD) said.
"Very dense" fog began forming at around 5.30 am, casting a thick haze over various parts of the national capital, the IMD said.
"By morning, a heavy layer of fog blanketed the city, reducing visibility to as low as 125 metres in certain areas," the IMD official said.
Meanwhile, the air quality remained in the "very poor" category for the 15th consecutive day, with a reading of 366 at 9 am.
Two monitoring stations, including Anand Vihar and Aya Nagar, reported the air quality in the "severe" category, according to the Central Pollution Control Board.
Humidity was recorded at 92 per cent at 8:30 am.
The weather department has forecast shallow fog for the day, with the maximum temperature expected to settle at 32 degrees Celsius.
