There is currently no service on the Central line westbound between Leytonstone and Liverpool Street.
Westbound passengers are being advised to take alternative routes following a signal failure at Mile End station.
Tickets are being accepted on London buses, Greater Anglia services, Chiltern Railway and Docklands Light Railway (DLR) services.
A spokesman for Transport for London said: "Emergency engineering works are taking place to Mile End to resolve this issue.
"We apologise for any inconvenience and the westbound service between Leytonstone and Liverpool Street is expected to resume in the next 30 minutes."