Delhi is covered with a thick blanket of fog, as many as 134 flights and 22 trains were delayed due to haze covered pockets of Delhi and its surrounding areas as mercury dipped to 6 degrees Celsius on Thursday morning.

The India Meteorological Department (IMD) predicted dense fog over Delhi, Uttar Pradesh, Haryana and Punjab till December 31.

At 5.30 am, visibility at Delhi's Safdarjung observatory dropped to 50 metres while Palam, near Delhi airport, reported a visibility of 25 metres. In Punjab, Haryana, Madhya Pradesh and UP,  the visibility ranged from 50 to 25 metres. The fog cover extended from Punjab to East Uttar Pradesh across Haryana-Delhi, West Uttar Pradesh, north Rajasthan and north Madhya Pradesh.

"Dense to very dense fog (0-25 meters) in some pockets of Uttar Pradesh and in isolated pockets over Haryana, Chandigarh & Delhi, Southwest Rajasthan and north Madhya Pradesh," the IMD said in a post on X.

The Met has predicted "very dense fog" for late night and morning hours till New Year's Eve in the northern states. Although Delhi saw improved visibility in some areas this morning, foggy weather continues to prevail in the NCR region.

"Fog likely to become more dense and very likely to extends more parts of Uttar Pradesh & north Rajasthan and some parts of extreme north Madhya Pradesh," the IMD said in a post on X, advising travelers to be careful and use fog lights while driving.

As cold wave conditions continue, the minimum temperature settled at 6 degrees Celsius while the maximum is expected to not go above 21 degrees Celsius.

The air quality remained "very poor" for the second day in the city. The average AQI in Delhi reached 386 with Anand Vihar recording an AQI of 464 in the "severe" category . According to the Central Pollution Control Board (CPCB), the pollution level will remain poor category for the next two days also.