Some lines have been blocked between Witham and Colchester, affecting services to and from Norwich.
As a result, services may be cancelled, delayed, or revised and the disruption is anticipated to last until further notice.
Emergency and Network Rail response teams are attending the scene.
The 6.30pm service from London was terminated early at Witham due to the incident and will no longer call at Colchester, Manningtree, Ipswich, Stowmarket, Diss and Norwich.