Visibility fell below 50 metres. The weatherman has forecast a further dip in temperature this weekend.
An official at the capital's Indira Gandhi International Airport said 30 domestic and 20 international flights were affected as the runway visibility range continued to remain well below 150 metres, the minimum required for flight operations.
"The visibility was poor due to fog and CAT III landing system was activated to help landing and take-off of flights, some of which were delayed, cancelled, diverted or rescheduled," the official said.
A Northern Railways spokesperson said 36 trains had been cancelled, 22 delayed and seven rescheduled.
There was chaos on the roads, as morning commuters crawled with their hazard lights on but still could not avoid the occasional bump into the next car due to poor visibility.
It became more serious in places where trucks had crashed into road dividers in the thick fog overnight. An incident of this kind on Ring Road in south Delhi's Lajpat Nagar closed much of one carriageway and led to a long traffic pile-up.
Delhi recorded a minimum temperature of 8 degrees Celsius, a notch above the average for this time of the year, though the damp weather made it seem colder. The maximum temperature is expected to hover around 18 degrees Celsius.
The weatherman has forecast thick fog on Saturday as well, with the minimum temperature at around 7 degrees Celsius.
An official at the Chandigarh weather bureau said: "This fog is due to the presence of excessive moisture and western disturbances in the atmosphere of northern plains."
It was freezing cold in parts of Punjab, and a further dip in the mercury has been forecast.Amritsar was the coldest city in the region Friday, with a minimum temperature of minus 0.2 degrees Celsius, four degrees below average. Ludhiana and Patiala cities in Punjab were comparatively warmer, with minimum temperatures of 5 and 5.7 degrees Celsius, respectively.
Chandigarh recorded a minimum temperature of 6.4 degrees Celsius."We are expecting a further decline in the night temperature whereas the day temperature will remain stable. Though we had bright sunshine in the region yesterday (Thursday), the intense cold wave subdued it," the official said.
In Haryana, minimum temperatures at Ambala, Hisar and Karnal cities were 5.1, 9.5 and 7.5 degrees Celsius respectively.