A dense layer of fog engulfed parts of the national capital Saturday morning reducing visibility to 100 metres, and affecting road and rail traffic.
The Safdarjung Observatory, the national capital's primary weather station, recorded the minimum temperature at 5.4 degrees Celsius, three notches below the season's normal, according to the India Meteorological Department (IMD).
A total of 14 trains were running late by 1.30 to 3.30 hours, railway officials said.
At 5:30 am, visibility was 100 metres at Palam and 200 metres at Safdarganj, two Delhi weather stations. Among other cities, it was 25 metres at Patiala (Punjab) and Ganganagar (Rajasthan), and 50 metres at Churu.
IMD officials said a layer of fog was seen mainly over Punjab, north Rajasthan, Haryana and Delhi. Another layer is seen over some parts of Bihar, while regions in Uttar Pradesh are free from the fog cover, they said.
According to the IMD 'very dense' fog is when visibility is between 0 and 50 metres, 51 and 200 is 'dense', 201 and 500 'moderate', and 501 and 1,000 'shallow'.
Meanwhile, humidity level at 8.30 am was recorded at 91 per cent, the weather department said, adding the maximum temperature is likely to settle around 20 degrees Celsius.
According to the Central Pollution Control Board (CPCB), the Air Quality Index (AQI) of the national capital stood at 364 at 9 am.
An AQI between zero and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor" and 401 and 500 "severe".