Two thieves stole a 70,000 euro (NZ$117,000) diamond ring from a Cannes jewellery store, pocketing the gem while a saleslady had her back turned, a police source said.
Police in the French Riviera resort town - which has been hit by a series of spectacular jewellery heists this year - said the men had eastern European accents.
They pilfered the ring from a jewellery store near the luxury Gray d'Albion hotel.
Police have opened an investigation and said they will examine security videos for evidence.
On July 28, an armed man pulled off a brazen heist in broad daylight at the luxury Carlton Hotel in the town, in one of the world's biggest jewellery heists.