Rail passengers travelling between Oxford and London Paddington are experiencing delays due to a signalling problem at Didcot Parkway.
CrossCountry and First Great Western services between Oxford and Paddington, and between Paddington and Didcot Parkway, are all affected.
Services are being held in the Didcot area while engineers work to resolve the problem.
A statement on the First Great Western website says: “Engineers are working as fast as possible to restore services to normal.
“Short-notice alterations, cancellations and delays of up to 60 minutes can be expected.
“Road replacement transport is being sourced. CrossCountry and Chiltern Railways are accepting First Great Western tickets on all reasonable routes.”
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