Borders Railway services have been disrupted due to a fault with the signalling system between Tweedbank and Stow.
ScotRail said problems were expected until about 19:00.
Trains services had resumed by 16:50 but passengers were warned some could still be cancelled, delayed or revised.
The company added that it would update its website regularly with information on how long any problems on the line might persist.
ScotRail apologised to passengers and advised any customers delayed for more than half an hour to make a claim to be refunded.