IndiGo and SpiceJet also said flight operations have been impacted because of bad weather.
At least 16 flights were diverted from Delhi to Jaipur, Lucknow, Amritsar, and Ahmedabad after operations at the capital's airport were impacted because of heavy rain and lightning, an official of Delhi's Indira Gandhi International Airport said.
Of the 16 flights diverted, 10 were rerouted to Jaipur, three to Lucknow, two to Amritsar, and one to Ahmedabad.
A Vistara flight from Guwahati to Delhi, UK742, was diverted to Jaipur due to bad weather and air traffic congestion at the Indira Gandhi International airport, news agency ANI reported.
Another Vistara flight from Kolkata to Delhi, UK 778, had also been diverted to Lucknow earlier in the day due to air traffic congestion at Delhi airport, the report said.
IndiGo also issued a "travel advisory" and said flight operations in Delhi had been affected by heavy rain.
"#6ETravelAdvisory : Flight operations to/from #Delhi are impacted due to heavy rain. You may keep a tab on your flight status by visiting ://bit.ly/2EjJGGT. For any assistance, feel free to DM," the airline posted on X, formerly Twitter.
A similar post was put up by SpiceJet, which warned that all arrivals and departures at Delhi airport may be affected.
The airline's post on X said, "#TravelUpdate: We are facing ATC congestion at Delhi (DEL) due to bad weather. All departures/arrivals and their consequential flights might get affected. Passengers are requested to keep a check on their flight status via http://bit.ly/2tG9xBx"
Residents of Delhi, meanwhile, hoped that the showers would bring down high pollution levels.
The city's air quality was nearing the severe category this morning with calm winds and cloudy conditions trapping pollutants, according to monitoring agencies.
The regional weather office had forecast light rain in a few areas in Delhi and surrounding regions.
India Meteorological Department (IMD) scientist RK Jenamani said the clouds over Delhi will persist till tomorrow, according to news agency PTI. The western disturbance created due to intense circulation over central Pakistan led to the cloud formation over Delhi, he said.
The minimum temperature was recorded at 13.4 degrees Celsius, three notches above the season's average.
The day began with a windy morning and a forecast for a cloudy sky with light rain. The relative humidity at 8.30 am stood at 97 per cent.