A person has been hit by a train near Llanbradach.
Services between Penarth, Cardiff Central and Rhymney were disrupted after the incident between Aber and Energlyn in Caerphilly on Monday night.
A spokeswoman for Welsh Ambulance Service confirmed they were called to the area but was unable to give any further details.
In a statement issued at around 7.30pm, National Rail said: "A person being hit by a train between Aber and Energlyn & Churchill Park means all lines are currently blocked between these stations.
"Trains between Cardiff Queen Street and Rhymney will be cancelled or revised.
"We anticipate disruption will continue until the end of the day."
Replacement buses were provided for passengers travelling between Cardiff and Rhymney on Monday night.