Travellers are facing delays of up to 50 minutes on the trains due to signalling problems near Chelmsford.
Trains travelling between London Liverpool Street, Chelmsford, Braintree and Clacton-on-Sea are affected.
Although the signalling problems have been fixed passengers are being warned that the delays could last until noon.
A replacement shuttle service was put in place between Braintree and Witham for the 10am service.
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