A forecast by the Met Department suggested that visibility may reduce to 0050 meters in very dense fog and it may improve to 0400 meters in moderate fog today at the IGI airport.
The fog, the thickest of the season on Wednesday morning, lasted for a maximum duration.
A news agency quoting an airport official said that around 20 flights were diverted to different airports including Jaipur, Chandigarh, Amritsar, Ahmedabad and Lucknow, due to the bad weather.
Trains from different parts of the country to the national capital are running late due to dense fog and poor visibility conditions today.
Over half a dozen passenger trains operating in north India were delayed Friday due to low visibility.
Visibility across North India was reduced to concerning levels as fog engulfed the entire region.
As many as 10 passenger trains are running late in the northern region due to low visibility, informed Railway officials on Wednesday.
According to a weather alert earlier, the approaching fresh cloud patches over Delhi was likely trigger a light to moderate spells of rainfall over the city.
Seventeen passenger trains in the northern parts of the country were running late due to low visibility and fog.
Several flights scheduled to depart from Delhi's Indira Gandhi International Airport (IGI) were delayed due to fog.
