Airport had witnessed the second longest duration of dense fog conditions in last eight years, which led to suspension of flight operations for about three hours on Sunday night.
A total of 463 flights were delayed, 52 diverted and 140 cancelled due to poor visibility due to dense fog, between 1 AM of Sunday night and 12 noon of today, airport officials said.
The heavy blanket of fog forced authorities to suspend flight movement at the IGI Airport for around three hours on Sunday night, leading to delay and diversion of around 150 domestic and international flights.
Between 8 PM last night and 8 AM this morning, around 150 flights, either arriving here or departing from here have been cancelled or diverted due to extremely poor visibility at the airport due to dense fog, an airline official said
As operations remained suspended, it led to cascading effect on the schedule of other morning flights and finally a large number of flights had to cancelled, the officials said, adding even the airlines were clue less and where finding themselves to handle the situation.
A SpiceJet flight from Goa to Delhi, with 132 passengers and four crew on board, had to make an emergency landing at around 9.50 PM as it ran short on fuel.
"Due to runway visibility range falling below 50 meters there were no flight operations on third runway (11/29) between 2100 hours to 0400 hours while on main runway (10/28) CAT IIIB conditions prevailed from 2030 hours to 0400 hours," DIAL said.
"We were left with no option but to cancel the flights, as there were huge number of flights got delayed due to diversions after they were unable to land at Delhi in poor visibility," the airline official said.
Lounges at the airport were packed with passengers who complained that they were not given information about the flight status.
Long queues were seen at airline counters for collection of refunds for cancelled flights or to get a seat on any early flight.
Around 15 flights coming to Delhi were diverted to Amritsar.
People could be seen moving from one counter to another in search of information or tickets.
"I had to wait for about three hours before the airline decided to cancel my flight to Mumbai. Now I am waiting in the queue to get a refund," said Anil Kumar.
One of the passengers, Anna, who was to arrive in Delhi from Hyderabad by an Air India flight which was subsequently diverted to Amritsar, said they have no clue when their flight will leave for Delhi.
"I have been waiting through the night at Amritsar airport. No idea when our flight will leave for Delhi. Authorities have told us that it might take off after noon," she said over phone from Amritsar.
The national capital has been witnessing thick fog since yesterday.
Airport Met In-charge, R K Jenamani, said that the fog spell from the night of January 4 when dense fog was observed from 2:30 AM till 10:30 AM of January 5.
"But on Saturday night, flights were not much affected and there were no diversions as city side of the main runway (10/28) was not affected due to dense fog," .
He said moderate fog, with visibility of 400-600 metres, remained all through the afternoon of January 5.
"But suddenly it became dense by 06:30 PM due to heavy moisture incursion to Delhi. The fog was so dense that it started closing the airport by almost 08:30 PM by bringing general visibility to 'zero' metres," he said, adding the runway visibility dropped to less than 175 metres due to which most of the flights could not take off.
Very dense fog layer stayed till 2:30 AM today, he added.
The minimum required visibility for an aircraft for the Low Visibility Take Off (LVTO) is 125 metres and 150 metres, depending upon the size of the aircraft.
Delhi airport is equipped with two CAT-III B complaint runways, which enables a CAT-III B trained pilot to land a CAT-III B complaint plane when the runway visibility is merely 75 metres.
Yesterday, the visibility remained poor during the whole day which led to delay in schedule of around 206 domestic and international flights.
Flight operations resumed today around 1 AM, when the landings started. Priority was given to international flights, as most of them operate at night, they said.
Though the visibility was poor, planes were landing using CAT III B ILS and the take off started around 4 AM, when runway visibility improved to more than 150 metres on the main runway (28/10), officials said.