Flight operations went haywire due to fog today at the Indira Gandhi International airport which remained closed for around five hours, affecting over 180 domestic and international flights.

The fog, which descended on the airport last night, grew denser this morning with the airport MeT department terming it the "worst" of the season.

Around 19 flights had to be 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, and 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 (sic)" 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.

Similarly, out of 19 cancelled flights, 12 were due to poor weather at Delhi, four due to bad weather at destination and three due to airlines operational reasons.

The visibility at the third runway (29/11) started to deteriorate from 1 AM, forcing the airport authorities to implement low visibility procedures (LVP).

The LVP was implemented on main runway at 4.10 AM and it was lifted from both the runways at 12.05 PM.

The airport witnessed huge backlog as no flights could take-off between 6 AM and 10.45 AM due to poor visibility.

The MeT department has predicted that the visibility may reduce to 500 metres in shallow fog from 10.30 PM tonight and further drop below 200 metres in dense fog from 2.30 AM tomorrow. It would further reduce below 50 metres in very dense fog from 6 AM tomorrow.

"Very dense fog developed over IGI airport during 4 AM to 10.45 AM when general visibility dropped below 50 metres. Thick fog started at western side of the airport at runway 29 end at 05.00 AM. It further deteriorated to below 50 metres at third runway 29. This was found to be worst dense fog observed in this season till superseding the earlier occurred dense fog date of 14 Jan of 2013," the official said.

He said a very active new western disturbance is likely to affect Delhi region during Feb 4 to 6, 2013 bringing good rainfall and cloudy conditions.

The present dense fog conditions over Delhi will significantly improve during next 48 hours with almost no dense fog on February 4 morning over the airport.