The Air Quality Index stood at 457 at 6am local time on December 15, according to data from the Air Quality Early Warning System for Delhi. Photo THE STATESMAN

NEW DELHI — A thick layer of smog and dense fog covered the Delhi National Capital Region (NCR) on the morning of Dec 15, pushing air quality into the “severe” range and affecting flight operations at the Indira Gandhi International Airport.

Several flights were delayed after visibility dropped sharply due to the fog. This was the first major spell of winter fog in the national capital this season, according to Indo-Asian News Service.

The Air Quality Index, or AQI, stood at 457 at 6am local time, data from the Air Quality Early Warning System for Delhi showed.

Visibility fell in many parts of the region, slowing early morning travel.

Dense fog over the city reduced visibility at Palam Airport in the early hours, leading airlines to issue travel advisories, United News of India reported.

According to available information, 40 flights were cancelled, while four others were diverted. Many flights were also delayed on arrival and departure.

Visibility fell to 100m at around 4.30am and may drop further to 50m. Light westerly winds of 5kmh to 7kmh were reported. The poor visibility affected flights.

“Due to dense fog, flight operations may experience disruptions. We are working closely with all stakeholders to minimise inconvenience to passengers. For the latest flight updates, passengers are advised to contact their respective airlines. We sincerely regret any inconvenience caused,” Delhi International Airport Ltd said in a passenger advisory.

Airlines such as IndiGo and Air India said they were watching the situation closely.

In messages posted on social media platform X, the airlines asked passengers to check their flight status before leaving for the airport. They said safety remains the top priority, and staff are available to help travellers.

“Low visibility and fog over Delhi will impact flight schedules. We’re keeping a close watch on the weather and doing our best to get you where you need to be, safely and smoothly,” IndiGo posted.

“We request you to stay updated on your flight status via our website or app. Be assured, our teams are here to assist you at every step and ensure support,” it added.

“Here’s hoping clearer skies help us serve you better soon, and thank you for your patience and understanding during this challenging time.”

Meanwhile, Air India also issued a travel advisory: “Poor visibility due to dense fog is impacting flight operations in Delhi and parts of northern India.”

Passengers were advised to plan their journeys carefully as weather conditions remained difficult. THE STATESMAN/ANN