London Northwestern Railway has said passengers should expect delays this afternoon.
It comes after a broken rail was detected between Milton Keynes and Northampton, meaning train services cannot run on that stretch.
A spokesman for London Northwestern Railway said at 4.15pm: "Due to a broken rail between Milton Keynes and Northampton, the line towards Northampton will be blocked.
"Please expect trains to be delayed or diverted via Northampton. We hope it will be over soon though."