Delhi recorded a minimum temperature of 8.4 degrees Celsius, one notch above the season's average, while dense fog affected visibility in several parts of the city on Thursday, according to the India Meteorological Department (IMD).

Reduced visibility also hit railway services, with 22 Delhi-bound trains delayed.

"Dense to very dense fog (0-25 metres) in some pockets of Uttar Pradesh and in isolated pockets over Haryana, Chandigarh and Delhi, Southwest Rajasthan and North Madhya Pradesh," the IMD said in a bulletin.

"Less than 30 metres of visibility was recorded in Patiala, Ambala, Chandigarh Haryana, Chandigarh, Delhi, Palam, Bareilly, Lucknow, Varanasi and Gwalior," it said.

In Delhi, the maximum temperature is expected to hover around 21 degrees Celsius, according to the department. The air quality of the city was in the "very poor" category.

The relative humidity at 8.30 am was 95 per cent in Delhi, the IMD said.

The IMD has also issued a dense fog warning for Haryana, Chandigarh and Delhi during the late and early hours until December 31.

In an advisory for dense fog, the department has asked drivers to use fog lights and travellers to stay updated on schedules of airlines, railways and state transport. "Exercise caution while driving or using any mode of transportation," the IMD said.

Central Pollution Control Board (CPCB) data stated that Delhi's overall air quality index (AQI) at 9 am stood at 377.

An AQI between zero and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".

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