Trains between London and Stansted Airport have been hit by the cold weather but flights are unaffected.
All train services between Stratford and Stansted have been cancelled.
And National Express East Anglia said a half-hourly service was running between London Liverpool Street and the airport instead of every 15 minutes.
The firm advised passengers to consult its amended timetable and said some other services in Essex were also cancelled.
Another train company, C2C, said all its services through Essex were running normally apart from one cancellation on Thursday.