The train line between Yeovil Junction and Exeter St Davids remains closed today due to a landslip.
Operator South West Trains had hoped the line may be able to reopen today, but heavy rain over the weekend has added to the damage.
"Our engineers are on site and are working hard to repair the damage caused by the flooding," said a statement on the South West Trains website.
"Due to the continued bad weather over the weekend, engineers have faced some setbacks to repairs and work undertaken.
"Engineers on site will continue to update us with information regarding when the line will reopen."
Train services that usually run between London Waterloo and Exeter St Davids are currently terminating at Yeovil Junction.
Buses are replacing trains between Yeovil Junction and Exeter St Davids in both directions, but South West Trains said they are subject to local weather and road conditions.
Disruptions also continue today on the train route between Taunton and Castle Cary, where flooding has blocked the Westbury-bound lines.
First Great Western is warning passengers of one-hour delays, diversions or cancellations.
There is also flooding between Exeter St Davids and Tiverton Parkway in Devon, and all lines are still blocked.
First Great Western said all stations between Exeter St Davids will not be served until 2am tomorrow morning at the earliest, and that limited bus services are available between Exeter St Davids and Tiverton Parkway.
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