There are major delays on the rail line between Chingford and Liverpool Street.
Services are currently terminating at Hackney Downs due to a signalling problem between Liverpool Street and Bethnal Green.
Services are also delayed by 20 minutes.
Greater Anglia has also warned some services may be subject to cancellation or alterations at short notice.
London Underground, buses, and First Capital Connect are accepting tickets on all reasonable routes
A spokesman for Greater Anglia could not give a time for when services will return to normal.
He said: "Thank you for your patience and understanding. Network Rail technicians are working as fast as possible to fix the problem."