After a day's respite, a thick blanket of fog again engulfed the Indira Gandhi [Images] International airport in New Delhi [Images] on Saturday morning causing inconvenience to passengers as 31 domestic and international flights were delayed, 19 were cancelled and three diverted to Mumbai [Images].

About 19 early morning flights for Chennai, Mumbai, Hyderabad, Jaipur [Images], Thiruvananthapuram, Bikaner, Ludhiana, Udaipur, Rajkot and Ahmedabad [Images] were cancelled as the general visibility dropped to below 50 metres and the runaway visibility range dipped to 100 metres in the wee hours, airport sources said.

This was much below the required minimum of 150 metres for the aircraft to take off in poor visibility conditions, they said.

After a relatively clear day on Friday, fog descended on the national capital shortly before midnight. It enveloped the airport area at 10 pm last night, forcing airport authorities to implement low visibility procedures.

Some of the international flights, which generally operate during the night from here, also got delayed due to the fog. Three international flights were diverted to Mumbai.

About 13 flights, mostly of Air India [Images] and Indigo [Images], took off for their destinations in CAT-IIIB conditions.

The fog situation began to improve at around 10 am, when the runway visibility range increased to 700 metres for main runway (28/10), while it remained 400 metres for the new runway.

Passengers were a harassed lot and said they had not received any information about their flights.

"I had to go to Kolkata for an urgent meeting, but my early morning flight was delayed by three hours and I don't know whether it will take off then," said P K Basu, a passenger.

He had left home at around 5 am to catch his flight and said he had not received any information regarding the delay.

Similarly, another passenger Pawan Sharma, who had to go to Lucknow reached the airport at 7 am for his flight that was scheduled to take off at around 9 am, but was delayed by three hours.

Sharma complained that he had not been informed by the airline of the delay and the flight information had not been updated on their website.

Fog has been affecting the flight movement in New Delhi since Monday and has led to the delay of more than 500 flights and cancellation of around 75 others.