After a few clear days, fog returned to blanket the national capital, throwing life out of gear. Traffic moved at a snail's pace and air and train services were badly hit.

Thick fog enveloped the national capital Thursday morning disrupting air and rail services and throwing normal life out of gear.

Hundreds of passengers were stranded at the Indira Gandhi International Airport (IGIA) as around 25 domestic flights and over 10 international flights were delayed for three to four hours owing to runway visibility dropping below 50 meters.

A minimum of 150 metres visibility is required for a flight to take off.

“The visibility was poor due to fog and CAT III landing system was activated to help landing and take off of flights, some of which were delayed, diverted or rescheduled,” an airport official said.

The rail services were also affected with as many as 24 trains to Delhi being delayed.

“Thirteen trains were cancelled due to the fog while another six were terminated short of Delhi. Nine trains have been rescheduled due to the inclement weather,” Northern Railway's spokesperson Anant Swarup said.

The trains rescheduled are North East Express, Taj Express, Himalayan Queen, Bhopal Shatabdi, Lucknow Shatabdi, Puri Express, Shan-e-Punjab, Delhi Jogbani Express and New Delhi-Mumbai Rajdhani.

According to an official at the India Meteorological Department (IMD), visibility recorded Thursday morning was 100 meters and the foggy condition is expected to continue till the afternoon.

The minimum temperature recorded was 6.2, one notch above average while the maximum is expected to hover around 19 degrees Celsius, two notches below average, the official added.

The minimum temperature Wednesday was 5.6 degrees Celsius while the maximum stood at 19 degrees Celsius.

Vehicular movement on roads was also slow, causing inconvenience to Delhiites while commuting.

The fog returned Thursday after four days of clear skies.