There were delays on the Norwich to London Liverpool due to a problem with overhead wires.
The problem started on the line between Colchester and Manningtree at about 10.45am resulting in disruption and the cancelling of some services.
The 12.30pm Norwich to London Liverpool Street service and the 12.30pm and 1pm services from London to Norwich were some of those cancelled.
A freight train was sent from Colchester to examine the wires and to help Network Rail understand the problem. Greater Anglia later confirmed a large branch had fallen on the overhead wires.
MORE: Rail services 'running normally' across Norfolk as second day of strike action gets underway
The line was reopened at 11.45am but delays to services are expected until 2pm.
Greater Anglia and Network Rail and apologised for the disruption to journeys.
It comes on the union members went on strike over the role of guards and driver-only trains. A spokesperson for Greater Anglia earlier claimed that services would be running as normal today.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here