About 12 domestic outbound flights were delayed by over 2 to 3 hours.
Five others filghts to Bhubaneswar, Mumbai, Shimla, Aurangabad and Lucknow were cancelled due to dense fog.
Five international flights coming from Dubai, Singapore and Beijing and same number of departing flights were also delayed by up to three hours.
According to airport officials, visibility further reduced to around 125 metres, while the general visibility remained below 50 metres.
"Flights were operating with help of CAT-III B instrument landing system," an airport official said.
The Delhi airport has been experiencing thick fog since Wednesday night, Jan 13, affecting the schedules of around 350 flights, causing inconvenience to air travellers.