Dense fog blanketed parts of the national capital that recorded a minimum temperature of 5.8 degrees Celsius on Wednesday morning.

The India Meteorological Department has predicted both "cold day" and "cold wave" in parts of Delhi on Thursday and Friday.

The visibility dropped to 100 metres in the Palam area in the morning, it said.

According to the 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 minimum temperature was three notches below normal. The maximum temperature is likely to settle around 19 degrees Celsius, it said, predicting 'cold day' conditions at a few places.

The IMD had declared a cold wave in Delhi on Tuesday as icy winds blowing from snow-covered western Himalayas brought the minimum temperature down to 4.1 degrees Celsius, the lowest in the city this season so far.

The maximum temperature had also dipped to 18.5 degrees Celsius, more than four notches below normal.

According to the IMD, the minimum temperature is likely to remain around five degrees Celsius till Friday.

Kuldeep Srivastava, the head of the IMD's regional forecasting centre said the Western Himalayas recorded widespread snowfall due to strong Western Disturbances and now frosty winds have been blowing towards the plains, bringing the mercury down.

He said both "cold wave" and "cold day" conditions are likely in Delhi on Thursday and Friday.

For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than normal for two consecutive days.

However, for small areas such as Delhi, a cold wave can be declared if the criteria are fulfilled even for a day, Srivastava said.

A cold day is when the minimum temperature is less than 10 degrees Celsius and the maximum is 4.4 degrees Celsius below normal.

The air quality was recorded in the "poor" category.

The city's air quality index (AQI) was 278 at 9 am. The 24-hour average AQI was 230 on Tuesday. It was 160 on Monday, 305 on Sunday and 356 on Saturday.

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".