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 7am and 8am was less than 200 metres and improved around 11am.
"Flights to and from Delhi may get delayed by up to 2 hrs due (to) runway closure for maintenance," Vistara tweeted.
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.