Flight operations, however, were normal, according to the official website of the Indira Gandhi International Airport.
At 5:30 AM, visibility was recorded at 500 metres, which dropped to 400 metres three hours later, a MeT department official said.
The minimum temperature settled at 7.5 degrees Celsius, considered as normal for the ongoing season. The relative humidity was recorded at 97 percent at 8:30 AM.
"A total of 52 trains were running behind schedule by several hours due to fog. These included Rajdhani Patna and Rajdhani Bhubaneswar," a railway official said.
"The maximum temperature is expected to hover around 23 degrees Celsius," he added.
Yesterday, the maximum and minimum temperatures were recorded at 23.4 degrees Celsius and 9.3 degrees Celsius respectively.