New Delhi (PTI): After a day's break, fog returned with a vengeance to the national capital on Thursday badly affecting air and rail traffic with over 76 flights being delayed and 18 cancelled and more than 25 trains running behind schedule.

Flight operations at the Indira Gandhi International airport here came to a standstill with the general visibility falling below 50 metres and runway visibility range (RVR) dipping to 125 metres, lower than the required minimum of 150 metres for the planes to take off, sources at the airport said.

Around 40 outgoing domestic flights and 15 incoming ones were delayed by up to five hours, while 11 international flights arriving at the IGI airport and 10 departing from there were also delayed, the sources said, adding that 18 flights were cancelled.

Several trains approaching the national capital were running several hours late, with some behind schedule by up to 20 hours, railway sources said.

The trains running late included Goa Express, Mumbai- Firozpur Express and Vaishali Express.

North-east Express and Dibrugarh Rajdhani from Delhi have been rescheduled, they said.

Barring a few, most of the early morning flights were either delayed or cancelled as the fog began enveloping the IGI airport from 1.30 am.