Though a police official couldn't confirm the jewels' worth to CNN, he did have details about the Sunday morning hold-up, in which an armed robber wearing a hat and scarf threatened to shoot exhibition guests at the luxurious Carlton Hotel.
"A full and urgent operation is under way to catch the culprit and recover these jewels. Thieves see Cannes as rich pickings," an official said.
Jeweler Leviev owned the diamonds on display, which if worth $53 million, would make Sunday's heist the second largest in French history.
BBC News notes that the famed hotel is the setting for Alfred Hitchcock's 1955 film, "To Catch a Thief."
During the Cannes Festival last May, a $2.6 million necklace was stolen from a hotel party and $1 million worth of jewels was stolen from a hotel room.
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