A signalling fault at Norwich is causing delays to train services in and out of the station.
Trains between London Liverpool Street and Norwich, in both directions and between Norwich and Cambridge, in both directions are being delayed by this fault.
East Midland services in and out of Norwich are also affected by this problem.
Trains running to and from the station may be cancelled or delayed by up to 30 minutes.
A Network Rail team are on site but delays are expected until 6pm.
In a statement on their website Greater Anglia said: 'Customers holding Advance Purchase tickets may travel on alternative services, if your designated train does not run.
'Network Rail engineers are at the location of the problem, known as a Track Circuit Failure and are investigating the cause, to enable a repair to be made as quickly as possible.
'We are sorry if your travel plans are affected by this disruption.'
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