Dense fog enveloped the Indira Gandhi Airport on Friday morning, leading to the diversion of four flights and delaying 75 others.
Two Jet Airway flights from Doha and Abu Dhabi and one Kingfisher flight from Dubai were diverted to Jaipur while one cargo flight from Chennai was diverted to Ahmedabad, airport officials said.
Ten flights were cancelled due to operational reasons or poor weather conditions at the destination. The fog started to descend at nearly 2 am leading to dip in the runway visibility.
The runway visibility decreased to less than 100 meters due to which flights could not depart as the permitted low visibility take off minima is 125 meters and 150 meters for various types of aircraft.
"Due to this, flights could not take off as per their schedule," the official said.
As the visibility improved, some flights took off but operations were again stalled when visibility dipped again, he said.
According to the Met department, the visibility is likely to improve after 11 am.
On Thursday, 266 flights were affected due to poor weather conditions.