Commuters on the Greater Anglia line from Liverpool Street to Shenfield face a long rush hour of cancellations and delays.
Services through Ilford, Romford and Chadwell Heath are being affected.
An “incident” at the train depot in Ilford is stopping trains getting in and out.
Operators have not confirmed what happened but said an investigation was ongoing.
An Abellio Greater Anglia spokesman said: “Due to a problem with a train in Ilford depot which is affecting access in and out of the depot, some of our services this evening have been cancelled.
“We apologise for the inconvenience caused and we are working to restore the normal service as quickly as possible.”
The incident, shortly after 5pm, coincided with Greater Anglia’s website going down but updates are still available on the National Rail website.
The following services were cancelled and others could be affected.
17:12 Liverpool Street - Witham
17:22 Liverpool Street - Southminster
17:38 Liverpool Street - Ipswich
17:52 Liverpool Street - Gidea Park
18:16 Witham - Liverpool Street
18:36 Southminster - Shenfield
19:10 Liverpool Street - Shenfield
19:18 Liverpool Street - Clacton
19:23 Ipswich - Colchester
19:32 Liverpool Street - Harwich International
Tickets can be used on the London Underground and local buses.
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