According to the India Meteorological Department (IMD), visibility dropped to less than 50 metres in some parts of the city at 8.30 a.m.
As a result, over three dozen incoming and outgoing trains were delayed or had to be rescheduled.
"There are 37 trains which are running late by two to 11 hours and one has been cancelled," said Northern Railway official.
The heavy fog also affected flights, leading to suspension of operations at the Indira Gandhi International Airport for over an hour Wednesday morning.
"We had to suspend operations due to bad weather and poor visibility for about an hour and a half. The flights resumed at 8.30 a.m. after visibility improved," said Kapil Sabarwal, spokesperson of the airport.
Traffic was heavy on several arterial roads of the city as motorists drove with extra caution.
The IMD has forecast a sunny and clear afternoon and said the fog is set to return in the evening.
"The afternoon will be sunny but there will be heavy fog late evening," said an IMD official, adding that the day's maximum temperature will settle around 23 degrees Celsius.
Wednesday's minimum temperature was a notch above the season's average at 8.9 degrees Celsius.
The national capital has been witnessing dense fog since Monday and as per the Met Office, there will be no respite for the next few days.
Tuesday's maximum temperature was recorded at 22.6 degrees Celsius, average for this time of the season. The minimum settled a notch above season's average at 9 degrees Celsius.
--IANS (Posted on 18-12-2013)