Sources at the Indira Gandhi International Airport said that due to low visibility on the shorter runway 9/27, they could only use runway 10/28 in the morning.
The third runway 11/29 is shut from today for three days for maintenance.
The official added that the second runway was opened after visibility improved.
According to officials of the India Meteorological Department, runway visibility between 7 am and 8 am was less than 200 metres and improved only at around 11 am.
"Flights to and from Delhi may get delayed by up to 2 hrs due (to) runway closure for maintenance," Vistara tweeted.
The smog has added to the woes of people flying in and out of Delhi as the airport is operating at 70 per cent of its capacity because of maintenance work on one of its runways.
The airport will be handling 800 flights per hour instead of 1,100 as airlines were told to curtail operations for three days. This means passengers will have fewer flight options to book as well as an increase in demand from travellers.