All trains heading from Worcester towards Cheltenham Spa have been cancelled or delayed.
An incident involving emergency services in Gloucestershire has meant that trains heading towards Bristol or Cardiff from Worcester are unable to pass.
A spokesperson for National Rail said: "The emergency services are dealing with an incident in the Cheltenham Spa area.
"Whilst they carry out their work all lines are closed. As a result, trains can be cancelled, severely delayed or revised.
"This is expected until the end of the day."
Rail replacement transport between Worcester Shrub Hill and Gloucester has been organised by GWR.
The replacement services will stop at Ashchurch and Cheltenham Spa.
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