Trains between Norwich and London are being disrupted after an incident on the line.
Greater Anglia has said they are investigating an issue between Chadwell Heath and Romford, which caused all lines to be blocked.
Emergency services are at the scene and are dealing with the incident.
Greater Anglia had advised rail passengers not to travel due to the congestion building on the route.
The line is now open but disruption is expected through the day.
A Great Anglia spokesperson said: "Following the emergency services dealing with an incident near the railway, all lines are now open between Chadwell Heath and Romford. All lines are now open and we will now work to get services running normally again."
Services could be cancelled, delayed or revised, and disruption is expected until 4pm.
Greater Anglia tickets are being accepted on London Underground services between London Liverpool Street and Kings Cross and Great Northern Services between London Kings Cross and Cambridge. Passengers can travel to Norwich via Cambridge.
Greater Anglia tickets are being accepted on c2c services between Southend Central and Fenchurch Street and London Underground services Fenchurch Street to Liverpool Street.
Network Rail and British Transport are on site.
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