Here are the latest developments:
At least 23 flights have been delayed while five have been cancelled in Delhi's worst fog of the season yet. 50 trains are running late while 12 others have been rescheduled.
At 4.2 degrees Celsius (four degrees below normal), Delhi woke up to its coldest morning in five years on Monday.
On Sunday, the maximum temperature in the capital plunged to 15 degrees, seven degrees below normal.
The Met department has said intense cold conditions will continue across the northern region. In Delhi, cold day conditions are expected, which means maximum temperature of less than 16 degrees.
On the other hand, parts of Madhya Pradesh and the Saurashtra and Kutch region in Gujarat are likely to experience cold wave conditions, which means a maximum temperature of less than 10 degrees.
The Met department has also forecast fog in Delhi and in Uttar Pradesh for the whole week. In Kanpur in UP, people were stranded early morning at railway stations as trains got late because of dense fog.
One person died of the cold in UP on Sunday. In Delhi, three people died of suffocation after they lit a coal fire to keep their home warm.
In UP's capital Lucknow, all schools have been ordered to close.
In Jammu and Kashmir, Chillai-Kalan - a 40-day period seen as they harshest part winter - began on Sunday, increasing the chances of the first snowfall of the season in the Valley which has had cold and dry weather so far.
A thick blanket of fog disrupted normal life in Punjab and Haryana too; air, rail and road traffic were hit.
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