A routine Network Rail inspection on Sunday found that a section of track at a railway junction was damaged.
A crossing – the curved rails which allow trains to move between tracks – is now being fixed on the West Coast Main Line near Wolverton.
It means London Northwestern Railway services travelling northbound are unable to serve Wolverton station. To keep passengers moving a rail replacement shuttle is operating between Milton Keynes Central, Wolverton and Northampton.
Passengers are being advised to use the rail replacement transport or to start their journeys from Milton Keynes while the repairs continue. It also means slightly longer journeys for passengers travelling northbound, with services being diverted via Milton Keynes.
James Dean, Network Rail’s West Coast South route director, said: “We’re sorry to passengers being impacted by the track fault at Wolverton. Crossings are heavily used pieces of track and are complex to repair, and this will take several days.
“Teams of engineers are working as fast as they can to repair the problem. In the meantime, I’d urge anyone travelling to check National Rail Enquiries or with London Northwestern Railway for the latest travel information.”
Lawrence Bowman, customer experience director for London Northwestern Railway, said: “We thank our customers making essential journeys this week for their patience while Network Rail works to repair the damage to the railway."
He added: “Passengers requiring northbound services from Wolverton are advised to consider travelling from Milton Keynes Central if possible, or to make use of rail replacement transport.”
The repairs to the railway crossing are expected to take until the end of this week.
Passengers making essential journeys are being advised to check www.nationalrail.co.uk .