Services have been suspended following an incident between Bridgend and Cardiff that has resulted in the closure of the railway line.
Routes travelling via Barry are particularly affected.
Trains between Bridgend and Rhymney will be revised to start and terminate at different stations.
Disruption is expected to continue until 1pm this afternoon.
Transport for Wales said: “You may be entitled to compensation if you experience a delay in completing your journey.
“You should keep your train ticket and make a note of your journey, as both will be required to support any claim.”
Buses are replacing trains between Bridgend and Barry, with Watts coaches expected to run at 9 minutes past the hour from Barry and 40 minutes past the hour from Bridgend.
Passengers were advised to check station signage or use National Rail’s online ‘Find a Station’ tool to locate pick-up and drop-off points for the replacement services.
Transport for Wales confirmed that their services between Bridgend and Cardiff Central, via Barry, are affected by the disruption.
Customers are directed to use the Transport for Wales Live Map to check services running in the area.
Affected passengers are reminded to retain their tickets and note down their journeys in order to claim compensation for delays, as advised by National Rail.
