Thieves broke into the room of a Chopard employee, opened a safe and made off with the jewels, police said.
The robbery took place at the Novotel hotel in the centre of Cannes.
Geneva-based Chopard is one of the official sponsors of the festival.
The jeweller redesigned the festival's Palme d'Or award and each year creates jewellery sets for the "mounting the steps" ritual of movie stars and directors.
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