The aircraft came down at around 13:40 local time in the Verdon Gorge, an area popular with hikers.
The helicopter, reportedly a Cougar, belonged to aviation company Eurocopter and was on a test flight involving pilots and engineers, officials say.
Witnesses said the helicopter had hit an electricity cable before plunging down onto the river bank.
Firefighters and a team of climbers were dispatched to the scene, as well as a medically-equipped helicopter.
The helicopter came down in one of Europe’s best known river gorges, which runs 700 m (2,300 ft) deep.
Police spokesman Benoit Gounine told reporters that rescuers had trouble reaching the site.
“The accident happened in a very difficult place to access, which complicates our work,” he said.
Investigations are taking place to determine the cause of the crash.
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