The national capital continued to reel under severe cold conditions on Sunday morning as the minimum temperature dropped to 3.5 degrees Celsius -- this winter's lowest -- and a thick layer of fog was seen in several parts of the city, weather officials said.

This was a marginal dip from Saturday's 3.6 degree Celsius and Friday's 3.9 degrees Celsius -- both of which were the season's lowest on the day.

Delhi's minimum temperature recorded on Sunday was four notches below of the season's average, according to the India Meteorological Department (IMD).

The IMD has predicted very dense fog and cold wave conditions for more two days in the national capital. The city could see dense fog till January 20, it said.

The Palam Observatory near the Indira Gandhi International Airport in Delhi reported dense fog with visibility levels plunging to zero metres by 5 am. The IMD said that it is the longest duration of dense fog this season.

The Indian Railways on Sunday said that 22 Delhi-bound trains were delayed by one to six hours due to the 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".

Delhi's overall Air Quality Index (AQI) stood at 458 under 'severe' catagory at 9 am, according to the Central Pollution Control Board (CPCB) data.

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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