The fog, which descended on the airport last night, grew denser this morning with airport MeT department terming it the "worst" of the season.
Around 19 flights had to diverted to Jaipur, Ahmedabad and Mumbai after visibility dropped to less than 50 metres in the morning while 19 were cancelled and around 130 flights were delayed by upto seven hours, an airport official said.
The fog started to envelope the airport from 8.30 PM last night but it become more dense around 1 AM but the visibility become almost zero between 8 AM and 8.30 AM.
"The runway visibility dropped to below 50 metres on both the runways rendering them inoperational," an airport official said.
Flights operations remained closed between 6 AM and 10.45 AM, after runway visibility was less than the required minimum of 50 to 75 metres for landing with the help of Category III B (CAT-III B) instrument landing system (ILS). The required minimum for a flight to take-off is 125 metres and 150 metres for light and heavy aircraft.
Out of the 19 diverted flights, three were diverted to Ahmedabad, one to Mumbai and 15 to Jaipur. Most of them were diverted due to visibility remaining below the required minimum. But three were diverted due to captain trained to operate in CAT-III B conditions, while one due to aircraft not being CAT-III B compliant.