White gowns dominated at the Cannes screening of Nebraska.
Heidi Klum, Nicole Kidman and Elsa Zylberstein all wore stunning pale floor length dresses.
A Cannes police source said authorities were investigating whether a second incident of vanishing jewels was a theft, a problem of inventory or a loss, a source said.
Another Swiss jeweller, Chopard, had gems worth $1.4 million stolen in the first week of the 12-day festival on the French Riviera.
Police said the Chopard jewellery had been in the safe at Suite Novotel hotel in central Cannes, which had been rented by an employee of the jeweller.
The entire safe was removed from the wall and taken during the night of 16 May.
Someone entered without forcing the door, a police source said.
A spokesman for Chopard, a sponsor of the Cannes festival, later played down the report, saying values had been exaggerated.
Jewellers and fashion houses use the world's largest film festival at Cannes as a promotional showcase, lending gowns and accessories to celebrities who are photographed.
The Cannes Film Festival was hit by a second suspected jewellery heist when a diamond necklace worth 2 million euros (£1.6 million) vanished during a star-studded party, according to upmarket jeweller De Grisogono.
Fawaz Gruosi, the founder of the Swiss firm, said the necklace was part of the company's 20th anniversary collection paraded by 20 models at the glitzy event at the Hotel Du Cap-Eden-Roc in Antibes outside Cannes on Tuesday night.
Sharon Stone and Paris Hilton were among the guests.
Mr Gruosi said 80 bodyguards, local police, hotel security, and De Grisogono staff had been on duty but when a check was made at the end of the night the diamond necklace was missing.
"We don't know exactly what happened ... it was one of the most beautiful items we had," Gruosi told said
A live outdoor television broadcast from the Cannes Film Festival was briefly interrupted when what sounded like gunfire sent the crew and audience running for cover.
Actors Christoph Waltz and Daniel Auteuil were among guests being interviewed on the programme 'Le Grand Journal' when what sounded like gunfire rang out.
Television footage shows Auteuil and Academy Award winner Waltz - a member of the Cannes festival jury - scrambling from the seaside stage with dozens of others as a someone was heard saying "there's someone shooting."
When Friday's programme carried on a few minutes minutes later, host Michel Denisot said the noise had been caused by blank rounds. There were no reports of injuries.
A man was detained by police with a starter's pistol, a pocket knife and a plastic grenade.
French police say thieves raided the hotel room of a representative of Swiss jeweller Chopard and made off with jewels.Read the full story ›
Swiss jeweller Chopard has issued a statement clarifying earlier media reports surrounding the robbery of jewels from a Cannes, where the annual film festival is taking place:
An employee of the Chopard house has been the victim of a robbery last night, in their hotel room while they were not on the premises.
They is currently a police investigation underway but we can let you know the value of the pieces stolen is far lower than that which is circulating in the media.
The jewellery stolen is not part of the collection of jewels worn by actresses during the film festival.
Thieves stole over $1 million worth of jewellery from the Novotel hotel in the centre of Cannes - where the annual film festival is taking place.
Swiss jeweller Chopard has loaned luxurious jewellery to celebrities in Cannes for the film festival, including actress Julianne Moore, model Cara Delevingne and singer Lana Del Rey.
It is unknown whether the jewels in the pictures below were among the items stolen by thieves.
Thieves who stole jewellery worth $1.2 million from a hotel in Cannes broke into the room of a Swiss jeweller Chopard employee, according to AFP.
The robbers reportedly opened a safe in the room and made off with the jewels, which were set to be loaned to celebrities who are in the French town for the annual film festival.
Swiss luxury watchmaker and jeweller Chopard is one of the official sponsors of the festival and they redesigned the Palme d'Or award, which is given to the director of the best feature film.
Jewellery worth more than $1 million (£650,000) has reportedly been stolen from a hotel in Cannes - where the annual film festival is currently taking place.
The jewels were set to be loaned to celebrities who are in the French Riviera town, according to reports.