The posh Mediterranean resort has fallen prey to thieves several times this year, notably during the film festival in May, which attracted a glittering array of celebrities from the movie world.
The value of the theft, which took place at 11am (0900 GMT) at the Kronometry store, is not yet known. The shop is one of many luxury stores on the beachfront Croisette avenue, and not far from the Carlton hotel -- the scene of a record $136-million (103-million-euro) robbery on Sunday.
It also sits opposite the building where the famed Cannes film festival is held every year. It had already been the victim of a one-million-euro heist in February, when robbers made away with some 150 watches.
Sunday's theft at the Carlton -- one of the biggest jewellery heists ever recorded worldwide -- stunned police and media with its simplicity. An armed man just walked into the hotel, which is popular with the rich and famous, and was once the location of Alfred Hitchcock's thriller "To Catch A Thief", and made off on foot with earrings, pendants and other jewellery from an exhibition.
The "Extraordinary Diamonds" show, put on by a group owned by Israeli billionaire Lev Leviev, was being held in a wing of the hotel that had direct access to the street. Authorities, workers and unions have since questioned security at the famed Carlton hotel, where managers have been accused of being "a little careless".
Police were not notified that the exhibition was taking place, which while not a legal requirement, is normally standard practice for luxury establishments like the Carlton.
Sunday's heist comes head-to-head with what is considered the world's largest ever haul of jewellery -- valued at around 100 million euros -- which took place in Belgium in 2003. It is also France's biggest jewellery theft.
But this is not the first time that Cannes has been the victim of spectacular robberies. In a pre-dawn heist at a hotel during the film festival in May, thieves stole jewellery worth $1.4 million due to be loaned to movie stars. That robbery took place in the hotel room of an American employee of Swiss jeweller Chopard while she was out for the evening, police said. In a scene straight from a Hollywood film, a strongbox containing jewels was ripped out of the wardrobe and carried off, they said.
In a second theft during the festival, robbers made off with a diamond necklace with an estimated value of $1.9 million. At least two apartments rented by film executives were also burgled during the 2013 festival, with thieves taking cash, jewellery and other personal items.
By Guylain Gustave Moke