Visibility is very poor in the city
A dense fog has enveloped the Indian capital, Delhi, leading to major disruptions in air and rail traffic.
At least 60 flights have been delayed or cancelled and more than 50 trains delayed, with visibility reduced to less than 100m (330ft) in many places.
Thousands of passengers are stranded at the airport and railway stations. The meteorological department said the fog was unlikely to lift before noon.
Severely cold weather has swept through northern India in the past month.
Reports say more than 400 people have died, with most deaths reported from the northern Uttar Pradesh state.
The fog, which descended on Tuesday night, became very dense at around 2230 (1700GMT) when general visibility dropped to zero.
Conditions worsened on Wednesday morning when visibility on the runway at Delhi's Indira Gandhi International Airport fell to 75m.
Road traffic was slow-moving and motorists were using their hazard lights.
Dense fog also disrupted rail and air traffic in parts of northern India on Tuesday.