While Brahmaputra Mail is running 12 hours late, Jansadharan Express and Magadh Express have been delayed by five and four hours respectively, a Northern Railways official said.
The departure schedules of Mahananda Express and Northeast Express have been rescheduled due to fog, according to the official.
Loco drivers are being instructed to run trains at low speed during foggy conditions.
Railways have already cancelled services of about 10 trains till January 16 in anticipation of dense fog during the period.