Engineers are trying to repair the fault at Loughborough, but East Midlands Trains is warning that a reduced service will operate while the work is carried out.
An East Midlands Trains spokesman said: "At present we are not sure how long repairs will take and when the line will open for us to run our full timetable.
"You should use alternative routes which remain the most comfortable and quickest journey options.
"Other train operators will accept East Midlands Trains tickets - Sheffield to London Kings Cross via Doncaster; Derby to London Euston via Birmingham; Nottingham to London Kings Cross via Grantham and Lincoln to Nottingham via Worksop or Newark.
"We are sorry for the delay to your journey today."