Heavy fog that engulfed New Delhi [Images] disrupted air services on Sunday, delaying about 18 domestic and international flights and leading to the cancellation or merger of 15 others.

Passengers complained that they did not receive any information regarding delays or cancellation of scheduled connections.

The visibility at the IGI airport this morning dipped to around 800 metres at around 12.30 am following which low visibility procedures were implemented.

Several airlines combined their early morning flights due to low passengers load and in anticipation of fog, which has been affecting the smooth flight operations since Monday.

Over 600 flights were delayed and about 100 cancelled this week due to dense fog that has been enveloping the national capital almost every alternate day.

"We have combined three morning flights due to low passenger load and also to ensure availability of aircraft at the other airports for smooth operations," said a spokesperson of an airline.

Flight schedule went haywires after dense fog descended the IGI airport on Saturday causing delay of about 150 flights and cancellation of 21 others.