The jewels were initially thought to have been loaned to stars at the annual film festival on the French Riviera.
They were taken from the hotel room of an employee of exclusive Swiss jewellers Chopard in the early hours of Friday morning.
Police say the thieves ripped the safe containing the jewels from a wall of the room at the Novotel hotel.
But a company spokeswoman, Raffaella Rossiello, insisted the value of the pieces had been exaggerated and "the jewellery stolen is not part of the collection... worn by actresses during the Cannes Film Festival".
And festival officials said the event's top award, the Palme d'Or, was not among the stolen items.
The trophy is also made by Chopard, an official sponsor of the festival.
Celebrities choosing the Swiss firm's gems for their red carpet appearances at this year's festival include Julianne Moore, Lana Del Rey and Cindy Crawford.
The theft happened a few hours after the festival was shown The Bling Ring, a new film by director Sofia Coppola.
The film is about teenagers who find out when celebrities are attending red carpet events in order to break into their homes and steal their designer clothes, bags and shoes.
More than $1m (£650,000; 777,000 euros) worth of jewels have been stolen from a hotel in Cannes, French police say.