Delhi's minimum temperature dropped to 3.5 degrees Celsius -- this winter's lowest -- on Sunday even as the India Meteorological Department said dense to very dense fog conditions are likely in the next two days.

The maximum temperature settled at 20.6 degrees Celsius, a notch above the season's average. On Saturday, the city's minimum temperature was recorded at 3.6 degrees Celsius.

According to the Central Pollution Control Board (CPCB) data, the overall Air Quality Index (AQI) at 4 pm stood at 447, which falls in the "severe" category.

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".

The IMD said the national capital has been in the grip of severe cold for the last three days and Sunday's was the lowest minimum temperature of this winter season.

The India Meteorological Department (IMD) has forecast mainly clear skies with dense to very dense fog for Monday morning. According to the prediction, the national capital is likely to experience dense fog and cold waves from January 14 to January 20.

Zero visibility was recorded at 5 am at the IGI Airport. The IMD said it has been the longest duration dense fog this season.

The Indian Railways on Sunday said 22 Delhi-bound trains were delayed by one to six hours due to dense fog in the national capital and several other states.

According to the weather office, "very dense" fog is when visibility is between 0 and 50 metres, between 51 and 200 metres is "dense", between 201 and 500 metres "moderate", and between 501 and 1,000 metres "shallow".

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