A thick layer of fog cloaked the Indo-Gangetic plains in north India on Tuesday, with poor visibility disrupting road and rail traffic.
Satellite imagery showed a dense elongated band of fog stretching from Punjab to the northeast.
A spokesperson for the railways said 30 trains arriving in Delhi were delayed by up to six hours due to foggy weather.
At 5:30 am, visibility levels stood at zero metres in Varanasi, Agra, Gwalior, Jammu, Pathankot and Chandigarh; 20 metres in Gaya; 50 metres in Prayagraj and Tezpur; 100 metres in Agartala; 200 metres in Amritsar; and 300 metres in Gorakhpur.
At the Palam Observatory near the Indira Gandhi International Airport in Delhi, visibility was limited to only 50 metres.
Early morning foggy weather in north and northeast India has heavily impacted road, rail and air traffic over the last fortnight.
On Monday, five flights were diverted and more than 100 flights were delayed at the Delhi airport.
Civil Aviation Minister Jyotiraditya Scindia said on Monday that all stakeholders are working round-the-clock to minimise fog-related disruptions.
The Delhi airport was asked to expedite the operationalisation of the CAT III-enabled fourth runway in addition to the existing CAT III-enabled runways.
Generally, CAT III compliance refers to flight operations in low visibility conditions.
As the blinding fog lowered visibility levels to zero metres at several places, the India Meteorological Department (IMD) advised people to avoid unnecessary travel and take precautions while driving.
The IMD said that dense to very dense fog conditions are likely to continue prevailing over north India for the next three days.
It said that cold day to severe cold day conditions would persist over the northern plains for two more days.
"Cold wave to severe cold wave conditions are likely to continue over northwest India for three days," it said.
In the plains, the meteorological office declares a cold wave if the minimum temperature dips to four degrees Celsius or when the minimum temperature is 10 degrees or below and is 4.5 notches below the normal.
A severe cold wave is when the minimum temperature dips to two degrees Celsius or the departure from the normal is more than 6.4 degrees.
A cold day is when the minimum temperature is less than or equal to 10 degrees Celsius below the normal and the maximum temperature is at least 4.5 degrees below the normal.
A severe cold day is when the maximum is 6.5 degrees Celsius or more below the normal.
