ECKWERSCHEIM, France — A high-speed train undergoing a test derailed, burst into flames, split apart and plunged into a canal in northeast France, killing at least seven people and gravely injuring at least 10 others in what officials said appeared to be an accident. There were no immediate indications that Saturday’s crash into the Marne au Rhin canal had anything to do with the deadly terrorist attacks in Paris a day earlier, said spokeswoman Viviane Chevallier of the Bas-Rhin region. Authorities believe the TGV high-speed train, with 49 people on board, was going too fast and skipped off the tracks in the town of Eckwerscheim near the German border, she said. In a statement, French President Francois Hollande’s office said the train was not running on a line used by commercial trains.