There are severe delays for train services into Cardiff after overhead electric cables were damaged.
The wires have affected the lines between Llandaff and Radyr, meaning any Valleys lines are unable to continue into the city centre.
Engineers and the British Transport Police at the scene.
Transport for Wales said repair work was underway but disruption is expected to last until 5pm.
In a statement, a spokesperson said: “Earlier this morning, a train struck overhead wires that had come down near Llandaf station. Engineers and the British Transport Police are in attendance to investigate and repair the damage.
“Services between Radyr and Cardiff have been affected as a result, with no services calling at Llandaf, Cathays or stations on the City Line between Radyr and Coryton. This is likely to be in place until this afternoon.
“We’re very sorry for the disruption to people’s journeys. We advise customers to check before they travel using the TfW website, app, or JourneyCheck page.”
Please note: services between Treherbert, Aberdare and Merthyr Tydfil and Cardiff are running but are being diverted where possible and may be subject to delays as a result.
National Rail said those with tickets between Cardiff Queen Street and Radyr via Cathays and Llandaff and also between Radyr and Coryton can use their tickets on Cardiff bus.