Three persons, including a woman, were killed in Ballia district, while one each died in Maharajganj and Barabanki districts since last evening, officials said.
In Delhi, residents woke up to a foggy morning and the minimum temperature settled two notches below normal at 5.9 degrees, Met officials said, forecasting a foggy morning for tomorrow.
Poor visibility due to dense fog affected air traffic at the IGI airport, with schedule of nearly 100 flights getting affected due to bad weather.
In Jammu and Kashmir, skiing resort of Gulmarg recorded a minimum of minus 7.6 degrees Celsius, while Pahalgam in south Kashmir recorded a low of minus 7.4 degrees Celsius.
Srinagar recorded a minimum of minus 4 degrees Celsius last night, the coldest of the season so far.
In Himachal, cold wave conditions continued to persist, with early morning fog engulfing most of the areas.
Mercury remained below normal by several notches in various parts and Keylong in the tribal Lahaul and Spiti district remained the coldest place at minus 10 degrees.
Punjab and Haryana also reeled under cold as minimum temperature dropped by two to seven notches at many places today, with poor visibility due to fog affecting rail and road traffic.
Hisar remained the coldest place in the region where mercury dipped to five notches below normal to settle at 1.8 degrees Celsius.
Amritsar shivered at a low of 2.2 degrees Celsius, two notches below normal and the minimum at Narnaul settled at 3.5 degrees Celsius, three notches below normal.