According to the railway authorities, more than 76 trains were running behind their schedule due to fog and poor visibility.

The trains that were hit by the fog are Farakka Express, Barauni Mail, Gomti Express, Shatabdi Express plying between Lucknow and New Delhi, Begampura Express, Shaheed Express, duplicate Punjab Mail and Prayag-Lucknow passenger.

The worst hit was Sadbhavana Express, running late by 22 hours, and Guwahati-Delhi Special which was 18-hours behind its schedule.

The Northern Railway has also announced cancellation of 16 major trains between December 21 and December 30. These trains include Kanpur-Prayag passenger, Prayag-Faizabad passenger, Sultanpur-Lucknow passenger and Lucknow-Kanpur Memu.

Regional Met Director JP Gupta, however, said the fog would subside considerably in the next two days. He also said the drop in night temperatures would stall "for a while".

But the weatherman also said the fog would be severe in the last week of December and during the beginning of the New Year.

Air traffic too was disrupted due to the fog. A Jet Airways flight between New Delhi and Lucknow and an Indigo flight between Lucknow and Mumbai was cancelled on Thursday.

An airport official said that the fate of these and other flights on Friday was uncertain.

The unrelenting cold wave continued in Uttar Pradesh, mainly due to the 'pachua' breeze at 10 km an hour, intensifying the cold wave in many parts of the state.

The Met Office said Western Disturbances were likely to aggravate cold wave conditions in the state in the next few days.