A train undergoing a trial on a new high-speed line from Paris to Strasbourg derailed on Saturday near the German border, killing 10 people, the local prefecture said.
Another 32 people were injured, 12 seriously. French Environment Minister Segolene Royal said at the scene that a further five were unaccounted for.
All those aboard the train were employees of the SNCF national railways. The accident was caused by excessive speed, although it was too early to say why the train was going that fast, the prefecture said.
Pictures from a Reuters photographer at the scene showed the locomotive partly submerged in a canal alongside the tracks with other parts lying broken and detached in a field beside the track.
Medical units including police divers were on the scene.
The second section of the Paris-Strasbourg high-speed TGV line on which the crash happened is set to open for service in April 2016.