STRASBOURG - Ten people were killed after a French high-speed train derailed during a test run on Saturday, local officials said, announcing a rise in the death toll.

The train accident happened “because of excessive speed” at Eckwersheim in eastern France as technicians were on board for testing, said a top local official Dominique-Nicolas Jane. However, police said the cause of the crash had not been determined. A source close to the investigation said dozens of technicians were aboard.

The accident is the worst since the French TGV trains went into service in 1981. A total of 49 technicians, but no paying passengers, were onboard when the accident happened during testing on one of the next generation of TGV high-speed trains due to go into service in Spring 2016, the local prefecture said. The train ended up near a bridge in the water of a roughly 40-metre (130-foot) wide canal.

A police dive team, helicopters and tens of rescue vehicles were sent to the scene in response to the crash. The initial toll was put at “at least five dead”.