A dense fog enveloped the national capital on Thursday morning. While flight operations at the Indira Gandhi International Airport were affected, four aircrafts arriving at the airport from different locations were diverted to other airports as they could not land in Delhi.

Flight operations at Delhi airport are "intermittent" but not "suspended", an airport official said. "The low visibility procedure was implemented at 3 AM. ATC is clearing arrivals and departures as per the fog situation," the official said.

In Mathura, due to the dense fog, 12 vehicles crashed into each other at the Yamuna Expressway. One person is dead while the others have been injured, reports ANI.

Earlier on Wednesday, the air quality index of the Central Pollution Control Board (CPCB) had Delhi's air in the 'severe' category with a reading of 410, which may affect healthy people and seriously impact those with existing respiratory ailments. A senior IMD official while talking about the prevalent condition said that the fog may mix with pollutants to turn into smog and this situation will persist for a couple of days.

(With inputs from PTI)