The incident in Luton has caused chaos between Bedford and St Albans with knock-on delays in the north of Northamptonshire.
The delays are expected to continue until the end of service, with replacement buses running between Corby and Kettering.
Passengers for Wellingborough may use buses between Wellingborough and Northampton.
EMT users are advised to travel on London Midland from Euston to Northampton, Cross Country or Virgin.
An East Midlands Trains spokesman said: “Although Network Rail engineers are attending the problem, we expect disruption to continue until the end of service.”