Flight operations were badly affected on Monday at the Indira Gandhi International airport due to heavy fog.
Around 15 flights were delayed and two cancelled and as many international flights were diverted to Mumbai.
A Jet Airways flight to Amritsar (9W3707) and its another flight for Lucknow (9W3319) were cancelled due to the heavy fog, while early morning flights to Bhubaneshwar, Chennai, Mumbai, Coimbatore, Bhopal were delayed by up to three hours, airport officials said.
Jordan Airlines' flight from Amman to Delhi and Jet Airways' Dubai-Delhi flight were diverted to Mumbai, they said.
The runway visibility range dropped to 75 metres on Monday morning, which disrupted flight operations, forcing the airport authorities to implement low visibility procedures.
However, some flights were operated using CAT-III B conditions, the officials said.
Amritsar is experiencing a heavy fog as minimum temperature there tumbled to 1.6 degrees Celsius on Sunday. Besides, the city also witnessed zero visibility throughout the day.
Delhi experienced a minimum temperature of 8.4 degrees Celsius on Monday morning, which is one degree above normal, the Met office said.
Most of the early morning flights to Bhubaneshwar, Chennai, Mumbai, Coimbatore and Bhopal were delayed by up to three to four hours, the sources said.
International flights from Kathmandu, Abu Dhabi and other destinations were also delayed. Some flights, mostly foreign-bound, operated with the help of CAT-III B flight operation systems, they said, adding the first domestic flight to land was from Indigo coming from Hyderabad.
Poor visibility forced airport authorities to initiate Low Visibility Procedures (LVP) when the range dipped below 800 metres. The fog played the spoil sport for the passengers who had planned to catch early morning flights.
Train services hit
Several trains, including Rajdhanis, to and from railway stations in Delhi were running several hours behind the schedule due to heavy fog that engulfed New Delhi.
The Rajdhanis running late included Mumbai-Delhi, Howrah-New Delhi, Rajindra Nagar (Patna)-New Delhi and Bhubhaneswar-New Delhi.
The Rajdhani trains were running two to three hours behind schedule.
"The delays are due to heavy fog in Delhi and other parts of north India. The trains are currently stranded at railways stations near Delhi," said a Northern Railway spokesperson.
The long distance trains running late due to fog were Gaya-New Delhi Mahabodi Express, Chennai Central-New Delhi Grand Trunk Express, Allahabad-New Delhi Prayagraj Express, Howrah-New Delhi Poorva Express and Udhampur-New Delhi Uttar Sampark Kranti Express.
These trains were running four to five hours behind the schedule.