Trains have been cancelled following a landslip, National Rail has said.
Services running between Blackburn and Bolton and on to Manchester have been called off following the incident near Darwen.
Manchester Victoria to Blackburn services are unable to go via Darwen and are being diverted via Todmorden where possible, the firm said.
A replacement bus service that will operate between Bolton and Blackburn in both directions and calling at all stations will extend journey times by 40 minutes.
