According to the India Meteorological Department (IMD), the visibility in Palam area dropped to zero between 4.30 a.m. and 6.30 a.m, and later remained less than 50 metres till 8.30 a.m. It only improved after 9.30 a.m. to 50 metres, the required range for an aircraft to land

An Indira Gandhi International Airport (IGIA) official told IANS that due to the low visibility, flight operations were badly affected between 5 a.m. to 10 a.m. .

"At least five flights were diverted and departures were affected till 10 a.m.," he said.

Trains that were delayed due to the dense fog cover included the Puri-New Delhi Purushottam Express (by over six hours), Gaya-New Delhi Mahabodhi Express and Howrah-New Delhi Poorva Express which were both held-up by more than five hours.

The minimum temperature in Delhi on Friday was recorded at 4.8 degrees Celsius, two notches below the season's average, while the humidity level was 100 per cent.

The city will witness shallow to dense fog throughout the day, the Met said.

The air quality in Delhi and adjoining areas turned 'severe' as the amount of moisture in the air prevented dispersal of particulate matters PM2.5 and PM10.

The overall Air Quality Index (AQI) of Delhi was recorded at 411, according to Central Pollution Control Board (CPCB).

Thursday's maximum temperature settled at 22.2 degrees Celsius, two notches above the season's average while the minimum was recorded at 4.2 degrees Celsius, three notches below the season's average.