Elizabeth line commuters travelling through east London are facing disruption for the whole of Thursday.
A speed restriction is in place over defective track at Ilford.
The issue is causing severe delays on the Elizabeth line between Shenfield and Paddington, according to TfL.
In a post on X, National Rail Enquiries said: “A speed restriction over defective track at #Ilford means that trains have to run at reduced speeds on some lines. “As a result, train services running through this station may be cancelled, delayed or revised.”
It said disruption is expected until the end of the day.
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Severe rush hour delays on the Piccadilly Line
06:49 , Josh Salisbury
In addition to the Elizabeth Line disruption, passengers are also facing delayed Piccadilly Line trains.
There are severe delays between Acton Town and Uxbridge due to a points failure at Northfields and minor delays en-route to Heathrow Terminals.
There are also minor delays on the Bakerloo as TfL engineers fix a signal failure at Lambeth North.
Elizabeth Line hit with delays
06:46 , Josh Salisbury
Good morning. Elizabeth Line trains running between Heathrow to Gidea Park in east London face disruption all day because of a defective track at Ilford.
The issue means trains have to run a reduced speed on some lines, with National Rail warning passengers of possible cancellations or delays of up to ten minutes.
TfL said there were minor delays on the line between Paddington and Shenfield over the track fault.