Following a fault with the signalling system earlier at London Liverpool Street, Greater Anglia said all lines were now open.
The company said services were returning to normal but some may still be cancelled, delayed by up to 30 minutes or diverted to and from Stratford.
The disruption is expected until 10am.
Greater Anglia said a major signalling equipment fault was affecting services into and out of platforms 1 to 10 at Liverpool Street.
A spokesperson said: 'Due to the nature of the fault this will affect all Greater Anglia and Stansted Express services into and out of Liverpool Street station.
'TFL Rail and London Overground are also affected by these problems.
'Some West Anglia and Stansted Express will be diverted and will run between Tottenham Hale and Stratford not serving Liverpool Street.
'Greater Anglia and Network Rail are sorry if your journey has been affected by this disruption.'
Specific train service alterations are available here at www.journeycheck.com/greateranglia/
Advance purchase tickets holders will be allowed to travel on earlier or later trains if their booked service is cancelled.
If your journey with us has been delayed by 30 minutes or more, you may be entitled to compensation for a portion of your fare.
Visit www.greateranglia.co.uk/about-us/our-performance/delay-repay for details.
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