Urgent repairs to the railway linking London, York and Scotland are taking place between Newcastle and Morpeth.
This means a reduced service will run between these stations as only 1 line is available for both northbound and southbound trains.
Services may be cancelled, or not call at Morpeth in the southbound direction.
Disruption is expected to continue until at least the end of the day on Friday 3 November.
This affects LNER and CrossCountry Trains to and from Edinburgh.
LNER is operating a reduced frequency service between Newcastle and Edinburgh.
Buses are replacing most Northern trains between Newcastle and Morpeth
TransPennine Express will be running a limited service between Berwick-upon-Tweed and Edinburgh. Trains from the North West and York to Newcastle will continue to run as scheduled.
Plessey Viaduct, is between Cramlington and Morpeth
During planned engineering work over the weekend, Network Rail teams discovered that the parapet, a safety feature installed on the bridge, had moved.
Work was stopped and specialist structural teams attended the site to assess options to repair the bridge.
Due to the site location, design of the viaduct, and the heavy machinery needed, moving the parapet back to its original location is not viable. Network Rail Structural Engineers and external specialists are working on different options to repair the structure.
The structure of the viaduct has not been affected and train services are still running on one line.
However, this does mean a reduced service is in place, as well as some bus replacement services, so passengers are urged to check before travelling via National Rail Enquiries or with their train operator.
Paul Rutter, Route Director for Network Rail’s East Coast route, said: “Our teams are working hard to repair damage to Plessey Viaduct. While we want to minimise disruption to travellers, the safety of passengers is our top priority.
“We are sorry for the inconvenience this will cause to journeys and we want to thank passengers for their patience and understanding while we carry out this vital work.”
A spokesperson on behalf of train operators said: “We want to thank our passengers for their patience as Network Rail carries out essential work to repair Plessey Viaduct.
“There is a reduced service in place, and some services are not stopping at Morpeth, Cramlington, and Manors stations.
“We are advising passengers to check before they travel with National Rail Enquiries or via their train operator.”