New Delhi, Dec 22 (IANS): Dense fog engulfed the Indo-Gangetic plains, including Delhi, for the fourth morning on the trot on Thursday, lowering visibility in the national capital and affecting traffic movement.

The national capital's Palam and Safdarjung airport logged visibility levels of 200 metres at 5.30 a.m.

"Low visibility procedures are in progress at Delhi airport. All flight operations are normal. Passengers are requested to contact the airline for updated flight information," stated the advisory issued for flyers by Delhi International Airport Limited (DIAL) on early hours Thursday.

Around 20 trains were delayed due to the thick fog and low visibility that blanketed the national capital this morning at the New Delhi Railway Station.

"Visibility at 8.30 hours IST, 0 meters in Bhatinda, Ludhiana, Patiala, Ganganagar, Bareilly had 25 meter visibility. Amritsar, Kernal, Chandigarh, Bahraich, Churu, Pantnagar, Lucknow, Purnea, Agartala had 50 meter visibility. Ambala, Hissar, Safdarjung, Palam, Patna, Supaul-200 m each while Mandi, Bhiwani, Ridge, Fursatganj, Jamshedpur, Panagarh, Cooch Behar, Haflong had 500 meter visibility," tweeted the India Meteorological Department (IMD).

The IMD has issued a 'cold wave' alert in many North Indian states.

A drop in temperature has been also recorded in states of North India, including Delhi, Uttar Pradesh, Punjab, and Bihar.

J&K's Srinagar city faced the coldest night of this season so far on Thursday at minus 5.5 degree Celsius as the minimum temperature.