General visibility dipped to 100 metres in several parts of the city affecting traffic movment. Cars moved slowly in the early hours of the day with fog lamps on and tail lights on the blink mode.
The minimum temperature in the capital was 12.3 degrees celsius, 4 degrees above normal, the Met office said.
A few flights were delayed at the Indira Gandhi International Airport as the Runway Visibility Range had dipped to 100 metres at 8:00 am.
The weatherman attributed the heavy fog to high-pressure area over the capital and adjoining parts that was affecting wind movement.
"The easterlies are bringing in moisture to the capital and a high pressure area is affecting wind movement leading to dense fog," the weather office said.
However, disruptions in air traffic were not severe as the RVR improved steadily and was 1150 metres at 10:00 am. Some early morning trains coming to the capital were delayed due to foggy weather.
Foggy conditions are likely to continue for another day, the weather office said.
At the airport, low visibility procedures were implemented at 8:00 am and flights operated using the Instrument Landing Systems. A thick blanket of fog had enveloped the capital on Saturday affecting road and rail traffic.
