Train services going from Plymouth to Newton Abbot have been cancelled due to flooding, Great Western Railway has confirmed.
The operator said the line towards Newton Abbot was closed.
High river water levels at Brent Mill Viaduct mean trains are only able to run on one of two lines between the stations, GWR said.
Disruption is expected until 18:00 GMT on Friday.
The operator said CrossCountry Trains and Stagecoach route X38 were conveying passengers via any reasonable route until further notice.