Train passengers in the South West are being advised to check before they travel due to some reduced services caused by the hot weather.
Great Western Railway (GWR) and Network Rail said they were aiming to operate most of their routes as usual on Thursday despite the amber heat warning, but warned there would be some changes to the timetables.
The train services between Truro and Falmouth are set to run hourly, instead of half-hourly, and the Okehampton branch line will be replaced by bus services.
The UK Health Security Agency upgraded the heat health alert for south-west England to amber from Tuesday to Friday, with temperatures forecast to reach 30C (86F) in parts of the region on Thursday.
The train services said the reductions would be made to ensure trains could run "efficiently and reliably".
The companies said trains between Exeter St Davids and Barnstaple would continue to run as normal.
GWR operations director Richard Rowland said he wanted to encourage everyone to "check their journey beforehand".
He said: "We want to keep our customers safe during the extreme heat, which is why we are taking the precautionary step of amending a small number of services at the hottest times of day.
"We know this could be disruptive to a few people and we're sorry for the inconvenience it will cause, but customer safety must come first."
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South West Train Services Reduced During Heatwave