Cable theft on the railway at Retford has led to delays of around 80 minutes on journeys between Doncaster and Grantham, according to Network Rail.
Signalling problems have arisen as a result of the theft, causing delays which are expected to come to an end at 3pm.
Services affected are:
* First Hull Trains between Beverley, Hull and London Kings Cross
* Grand Central between Sunderland/Bradford Interchange and London Kings Cross
* Virgin Trains East Coast between Edinburgh/Leeds/Hull and London Kings Cross
A spokesman for Network Rail said engineers are working to resolve the problem. Some services will be diverted.