Train services between Norwich and London were halted on Tuesday afternoon after power lines were brought down near the capital.
Network Rail, which maintains the track, is working to repair the lines at Seven Kings and restore power.
A spokesman for Anglia Railways said some trains bound for Norwich and other points east from London's Liverpool Street station were running during the evening commuter rush, but most were starting from Colchester.
Rail passengers were brought to Colchester via a Great Eastern shuttle connection.
The company said short notice alterations, cancellations and delays were expected.