The 11.09am, 11.40am and 12.09am trains from Gloucester to Yate (with some via Cam and Dursley) have all been cancelled.
A spokesperson for National Rail said: “A safety inspection of the track is taking place between Cheltenham Spa / Gloucester and Bristol Parkway, closing the line running towards Bristol Parkway.
“As a result of this, trains may be cancelled, delayed by up to 70 minutes, revised or diverted.
“Major disruption is expected to continue to impact services until 1pm.
“Great Western Railway customers may use their tickets on First Bus routes Y1 between Yate and Bristol, and also Y6 between Yate and Patchway at no extra cost.”
LATEST UPDATE as of 11.43am
A National Rail spokesperson added: “The earlier safety inspection of the track taking place between Cheltenham Spa / Gloucester and Bristol Parkway has now been completed, allowing the line running towards Bristol Parkway to reopen.
“As service recovers, trains may still be cancelled, severely delayed by up to 90 minutes, revised or diverted.
A Great Western Railway spokesperson added: “Where possible, trains will divert via an alternative route.
“Where this is the case, Cam & Dursley and Yate stations will not be served, and journey times will be extended.
“Great Western Railway are currently looking to source alternative transport for any customers at these affected stations.
“In addition to using the reduced Great Western Railway service, customers can use CrossCountry services (who are also diverting), or one of Great Western Railway’s London Paddington services from Gloucester, and then change at Swindon.
“You may use your ticket on CrossCountry services via any reasonable route at no extra cost.”