The Indian Meteorological Department (IMD) said that a dense to a very dense layer of fog has engulfed Punjab, Haryana, Chandigarh, Delhi, North Rajasthan and Uttar Pradesh, engulfing the Indo-Gangetic plains, including Delhi, for the second morning on the trot on Tuesday, lowering visibility to 50 metres in the city and affecting road traffic and train movement.
According to the India Meteorological Department (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.
The thick blanket of fog has resulted in poor visibility in several cities. Visibility dropped to 50 metres at the Palam and Safdarjung airports between 5:30 am and 7 am, an IMD official said.
The Met Office had on Monday forecast that the Indo-Gangetic plains may see "dense to very dense" fog over the next five days, which may result in the cancellation and diversion of trains and flights.
On Tuesday, 11 trains were reported running late by one to five hours. Flight operations, however, were unaffected, an airport official said.
Satellite images showed a thick layer of fog over Punjab, Haryana, Delhi, north Rajasthan and Uttar Pradesh.
"Due to moisture and light winds at lower tropospheric levels over Indo-Gangetic plains, dense to very dense fog in many/some pockets very likely over Punjab, Haryana, Chandigarh, Delhi, Himachal Pradesh and Uttar Pradesh in night/morning hours during the next three days and dense fog in isolated pockets for subsequent two days," the Met office had said in a statement on Monday.
The IMD also issued an advisory, saying difficult driving conditions on highways, some collisions and tripping of power lines are possible.
"Likely train delays, diversons and cancellations. Airport operations are likely to be affected with flight delays and cancellations," it said.
The weather department said long exposures to fog can cause wheezing, coughing and shortness of breath in people having asthma bronchitis. It could also lead to eye irritation or infection.
It suggested that travellers carry essential items like water and medicine on long journeys.
The Safdarjung Observatory, the primary weather station in Delhi, recorded a minimum temperature of 6.3 degrees Celsius, two notches below normal. The maximum temperature is likely to settle around 22 degrees Celsius.
The minimum and maximum temperatures are likely to drop to five degrees Celsius and 20 degrees Celsius in the next few days.
The MeT office had earlier said that many parts of northwest India may see a warmer winter season primarily due to likely subdued activity of western disturbances.
(with PTI inputs)