Commuters and passengers on Greater Anglia trains to and from Norwich are facing cancellations or delays because of problems on the line.
The problem is being caused by a points failure at London Liverpool Street station and some lines are blocked, according to Greater Anglia.
It added train services running to and from Norwich may be cancelled, delayed by up to 15 minutes or revised.
Disruption is expected until 10.30am.
Greater Anglia said: 'Due to a points failure affecting platforms 11 and 12 at London Liverpool Street, services will experience disruption until the points can be restored.
'Network Rail have closed a section of the track that affects platforms 11 and 12 to work on the set of points. Whilst they do this essential work, some of our trains will transfer to the other line towards London Liverpool Street.
'This will cause significant congestion on the approach to London, and services will be delayed and may also have altered platforms.'
As well as the London Liverpool Street services, Norwich to Great Yarmouth Greater Anglia services are cancelled because of a train fault.
The 8.09am service from Norwich and 8.46am service from Yarmouth are not running.
Visit www.greateranglia.co.uk for updates.
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