Teams from Network Rail have been working overnight to fix problems that have brought much of the region's rail service to a standstill.
Heavy rain has flooded the railway at Cowley Bridge, between Exeter St Davids and Taunton. Trains between these stations are currently unable to run - and that is expected to remain the case all day.
Great Western Railway is advising passengers not to travel unless necessary.
Where possible Great Western Railway services between London Paddington and stations in Devon & Cornwall are being diverted via an alternative route where resources are available.
There is currently no firm estimate as to when the line will reopen but it is expected that disruption will continue until at least the end of service today.
This is how services are looking
EXETER ST DAVIDS TO TAUNTON
Replacement bus service running on CrossCountry and Great Western Railway between Exeter St Davids and Taunton due to flooding. Tickets are being accepted on South West Trains and local bus services.
EXETER ST DAVIDS TO TIVERTON
CrossCountry and Great Western Railway trains are unable to run between Exeter St David's and Tiverton Parkway.
LONDON PADDINGTON TO DEVON AND CORNWALL
Where possible, GWR and CrossCountry trains between London Paddington and stations in Devon and Cornwall will be diverted via an alternative route.
EXETER ST DAVIDS TO BARNSTAPLE
No trains between Exeter St Davids and Barnstaple until the end of Wednesday 23 November due to flooding.
Limited replacement bus service on Great Western Railway between Exeter St Davids and Barnstaple due to flooding. Tickets being accepted on local bus routes.
LISKEARD TO LOOE IN CORNWALL
Buses replace trains on GWR between Liskeard and Looe until the end of Wednesday 23 November due to flooding.