People travelling between Chesterfield and Sheffield can expect delays of 20 minutes or even cancellations after a lorry has struck a bridge near Dronfield.
The accident has caused disruption to the East Midlands Trains service between London St Pancras and Sheffield.
An East Midlands Trains spokesman said: “Where possible our trains will be diverted between Chesterfield and Sheffield with extended journey times of 20 minutes. Short notice alterations and cancellations will apply to trains which are not able to divert around the problem.
“Network Rail are going to investigate the problem. They are expected to arrive on site at 1.30pm.
“At present we are expecting the line to fully reopen in the next 1-2 hours. Our normal train service is expected to resume on the affected routes at around 3pm.
“We are currently looking at alternative arrangements to keep you on the move.”