Some 2,300 rail passengers were stranded in stations in the south of France overnight after a power failure in the Var region.
Two high-speed trains running between Paris and Nice were brought to a standstill, in Toulon and Carnoules.
The trains reached their destinations on Sunday morning, passengers arriving in Paris 17 hours after leaving Nice.
The French state rail company called the power cut “unacceptable” and promised legal action.
The delays coincided with an ongoing nationwide strike by rail staff which has halted many trains.