Great Western Railway trains are currently delayed between Exeter, Taunton and Bristol due to cows on the line.
The line between Taunton and Tiverton Parkway has now re-opened, but as trains were cancelled earlier, the service is still expected to be disrupted until midday.
National Rail says there is 'major disruption' but lines have reopened following cattle on the railway between Tiverton Parkway and Taunton.
Trains running between Exeter St Davids and Taunton may still be cancelled, delayed by up to 40 minutes or revised whilst service recovers.
While the line was closed, South Western Railway was carrying passengers from Exeter to Waterloo via Salisbury, while Network Rail dealt with the cattle.
For people travelling from London to Exeter, the London Underground were also conveying passengers from Waterloo to Paddington to pick up the SWR line via Salisbury.
A spokesman for GWR said: "South Western Railway are conveying passengers between Exeter St Davids and London Waterloo via Salisbury in both directions until further notice.
"Arrangements have been made for Great Western Railway rail tickets to be accepted for these journeys.
"London Underground are conveying passengers between London Waterloo and London Paddington in both directions until further notice. Arrangements have been made for Great Western Railway rail tickets to be accepted for these journeys."
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