Derbyshire and Nottinghamshire trains to London St Pancras have been severely disrupted due to a signalling fault.
East Midlands Trains said alternative travel arrangements are in place for the disrupted London St Pancras, Nottingham and Sheffield route
Network Rail are at the site inspecting the fault. near St Albans.
An East Midlands Trains spokesman said: "Your journey may be delayed in excess of two hours. We are very sorry for the delay to your journey today.
"All of our trains on this route cannot run in either direction between London St Pancras - Luton Airport Parkway.
"All southbound trains will be terminate at Luton, and all northbound trains will start from Luton.
"There will be extended delays and cancellations to all services on this route. We do not currently have an estimate for when the line will reopen."
You may travel via the following alternative routes:
Sheffield - You may travel to Doncaster where you should change for a train to London Kings Cross
Derby/Chesterfield - You may travel to Birmingham New Street where you should change for a train to London Euston
Nottingham- You may travel to Grantham where you should change for a train to London Kings Cross
Leicester - You may travel to Nuneaton where you should change for a train to London Euston
Bedford - You will be able to travel on Thameslink services between London St Pancras - Bedford.
Wellingborough/Kettering - You will be able to use your tickets on Thameslink services to Luton and catch a connecting service to Wellingborough and Kettering.