The national capital has been enveloped by dense fog since Friday night, bringing down visibility to about 10 metres and consequently disrupting air, rail and road traffic.
All domestic flights were delayed and some international flights to Delhi were diverted to other cities due to the thick blanket of fog, Indira Gandhi International Airport sources said on Saturday.
A railways spokesman said trains were running late due to the foggy conditions in the northern region.
Vehicles on Delhi roads moved slowly with drivers using headlights and blinkers.
The meteorological department said the visibility was at its lowest of 10 metres between 0630 IST and 0830 IST.