The train ended up under a bridge in the water of a roughly 40-metre (130-foot) wide canal. killing at least 10 people.
37 people were injured, 12 of them in critical condition while 5 others are missing.
This is the first fatal accident since 1981 when the TGV (“train grande vitesse” or high-speed train) went into service in France.
AFP reported that, the train was running at around 350 kph (217 mph) on a high-speed line as part of testing for the next generation of TGV due to go into service in spring 2016, a source close to the inquiry said.
AFP also reported that Dominique-Nicolas Jane, a senior official in the Alsace region said that the accident happened “because of excessive speed” at Eckwersheim in eastern France as technicians were on board for testing.
However, police said the cause of the crash had not been determined.