The main rail line between Ipswich and Norwich has been closed during Thursday morning after a signalling fault near Stowmarket.
The rail company Abellio Greater Anglia are advising passengers wanting to travel between Norfolk and Suffolk not to travel or to delay their journey until the afternoon.
Train services which start at Ipswich heading towards London are not affected and Greater Anglia says a "very limited" bus replacement service is running between Ipswich and Stowmarket.
Network Rail engineers are on site at the location of the fault, and are working to determine the cause of the fault and make repairs to enable the trains to run.
Currently the fault means that trains are unable to run in both directions between Stowmarket and Ipswich.