Twenty-four trains were delayed after fog engulfed the national capital on Tuesday morning with the meteorological department forecasting light rains in the evening.
The minimum temperature settled at 9 degrees Celsius.
"Twenty-four trains were delayed with an average delay of around three to four hours," the railways said.
The trains delayed included the Malda-Delhi Farakka Express and Howrah-New Delhi Duronto.
The visibility at Safdarjung was recorded at 1,500 metres at 5.30 am and 1,000 metres at Palam, a meteorological (Met) department official said.
There were no disruption in flight operations at the IGI airport, a source at the Delhi airport said.
The Met office has forecast shallow fog for the day ahead with the maximum temperature likely to settle at 23.2 degrees Celsius.