No trains are running between Newcastle and Edinburgh for the next two weekends.
Network Rail said the line would be closed on 13 and 14, and 20 and 21 September, due to various improvement projects, including laying new track, drainage systems, switches and crossings.
LNER is diverting an hourly train in each direction via Carlisle, while putting on rail replacement coaches for people in Morpeth, Alnmouth, Berwick-upon-Tweed, Reston and Dunbar.
CrossCountry and TransPennine Express are running replacement bus services in place of trains, with passengers urged to plan their journeys in advance.
All Lumo services will operate between London King’s Cross and Newcastle only, while the late 20:56 BST Saturday service will not run.
Northern trains between Carlisle/Hexham and Morpeth/Chathill will terminate and start at Newcastle.
Meanwhile, replacement bus services have been put on between Newcastle and Morpeth/Chathill.
ScotRail trains between North Berwick/Dunbar and Edinburgh will be replaced by buses on Saturdays only.
Northumberland Line services between Newcastle and Ashington are unaffected.
LNER warned that alterations to its schedule would impact services to Peterborough, Doncaster and Durham.
Passengers have been told to check details of their journey with National Rail or their train operators before travelling.
Network Rail operations director Sam MacDougall said the works were to invest in the “future of rail in the North East”.
“We appreciate that this work will mean a couple of weekends of where some journeys will take longer than usual, and we’d like to thank passengers for their patience while we carry out these improvements.”