A total of 10 flights were diverted, nearly 100 delayed, and some cancelled at the Delhi airport on Sunday morning, as low visibility due to dense fog conditions disrupted operations.
An official said a total of 10 flights, including 2 international flights, were diverted to Jaipur between 4.30 am and noon.
Sources in the know said the visibility at the airport was almost zero during the period from 4 am to 10 am.
During this period, there were no flight departures and only 15 arrivals, they added.
The airport handles around 60 departures and arrivals per hour in normal weather conditions.
Sources also claimed that the 10 diversions were due to the pilots operating the flights concerned not being trained for CAT III landings.
Generally, CAT III refers to landing in low visibility conditions.
During the day, airlines said their flight schedules might be impacted due to adverse weather conditions.
The country's largest airline IndiGo said low visibility and dense fog conditions across north India had a "cascading effect" on its operations.
Among the impacted flights at the Delhi airport, Air India's flight AI 185 to Vancouver, slated to depart early in the morning, was rescheduled.
Passengers had to wait inside the aircraft for many hours before they deboarded.
After boarding was complete, the flight, which was to depart a little past 5.00 am, could not take off due to the dense fog.
An airline official said that after waiting for a few hours, it was decided to reschedule the departure of the flight as the crew would have also breached the flight duty timing requirements.
Now, the flight is expected to leave at around 11.30 pm. The passengers have been provided accommodation, the official added.
At 8.38 am, the Delhi airport said that due to dense fog, flight operations at the airport may get affected.
"Passengers are requested to contact the airline concerned for updated flight information," it said in a post on X.
A thick layer of fog shrouded Delhi and other parts of North India on Sunday, with visibility levels plunging to zero metres at several places.
In a statement, IndiGo said its flight operations were impacted due to the low visibility and dense fog conditions across north India.
"This had a cascading effect on our operations throughout the day. Our staff kept passengers apprised of all delays and cancellations across airports and made every possible effort to facilitate the passengers. We sincerely regret the inconvenience caused to our passengers," it said.
Vistara, in a post on X at 6.38 am, said that due to dense fog and poor visibility in Delhi, arrivals and departures may be impacted from Delhi.
"Due to adverse weather (fog) at Delhi, Chennai, Varanasi, Bagdogra & Lucknow our flight schedules have been affected, which may lead to consequential delays. We understand this may impact your travel plans and regret the inconvenience...," Akasa Air said in a post on X at 12.12 pm.
Meanwhile, in another post on X at 1.35 pm, Akasa Air said that due to fog in Varanasi, four flights have been cancelled. They are Bengaluru-Varanasi, Varanasi-Mumbai, Mumbai-Varanasi and Varanasi-Bengaluru flights.
During December 25-28 last year, flight operations were significantly impacted at the Delhi airport, and nearly 60 flights of various airlines were diverted due to dense fog.
Last month, airport sources had said that a total of 58 flights were diverted due to bad weather between 12 am on December 25 to 6 am on December 28.
Recently, aviation regulator Directorate General of Civil Aviation issued show cause notices to Air India and SpiceJet for not deploying pilots trained to operate in low visibility conditions, following diversions of various flights amid dense fog at the Delhi airport in late December.
