The accident took place about 70 nautical miles (about 130 kilometres) off the coast of Dunkirk on Wednesday night, when the combat helicopter attempted to take off from the Dixmude ship for a training flight, the military said in a statement on Twitter, without giving details.

The helicopter's crew escaped unharmed but four navy members working on the flight deck were injured, one seriously.

The seriously injured member was initially treated in the ship's hospital before being evacuated to a military hospital, the statement said, adding that the cause of the accident was being investigated.

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