The suicide by a train driver on the job has caused widespread delays in France's rail traffic, operator SNCF said on Wednesday.

Some 3,000 train passengers have been affected by delays in services between Paris and southeastern France that started on Tuesday and spilled over into Wednesday.

Around 10 high-speed (TGV) trains were delayed by up to five hours on Tuesday after the suicide on Christmas Eve, an exceptionally busy time for travel.

The prosecutor's office in Melun, southeast of Paris, said that the driver appeared to have jumped to his death from the moving train.

His body was discovered later near the tracks.

Without a driver operating the controls, the train's automatic emergency procedure kicked in, causing the train to stop, the office said.

An investigation into the circumstances of the death was ongoing.

SNCF confirmed the driver's death, saying he "committed suicide while the train was moving."

There was no threat to the safety of passengers on the train, or to services elsewhere in the network, SNCF added.

Train traffic was "resuming progressively" on Wednesday, SNCF said, warning however of some possible further delays. (AFP)