"The fog, which began to descend late last night, affected normal operations at the airport, delaying the flights and diverting one to Jaipur," a source at the airport said. Six flights were cancelled, it said.

Air India flight from Muscat to Delhi was diverted to Jaipur around 3.15 am when the general visibility was zero and the runway visibility range (RVR) was 100 metres.

The fog began to envelope the airport around midnight, when the visibility dipped to zero and the RVR to 75 metres for new runway (29/11) and 100 metres for main runway (28/10).

The "zero visibility" condition remained for about four hours from 1 am to around five in the morning, however, the RVR hovered around 100 metres. The situation began to improve around 6 am with the visibility increasing to 100 metres and RVR to 500 metres.

But the visibility dropped to 'zero' at 7.30 am again but the RVR remained at 275 metres and some flights operated under CAT-III B conditions.

On Sunday, over 50 flights were delayed while around 15 were cancelled and 23 others diverted to other destinations due to the fog.