Two men in suits and a woman raided a shop of the luxury Swiss watch brand Piaget in central Paris on Tuesday, escaping with between €10 million ($11 million) and €15 million worth of jewellery, the Paris prosecutors' office said.
The robbery took place about lunchtime while shoppers were in the shop. The bandits allegedly held staff members at gunpoint.
They left on foot and nobody is thought to have been hurt during the raid.
Paris prosecutors have opened an investigation for "armed robbery by an organising gang" and "kidnapping".
The shop is on the Rue de la Paix in the upscale Place Vendome area, home to several jewellers, watchmakers and luxury brands.
The area has experienced a spate of armed robberies in recent years.
Piaget is a luxury Swiss watchmaker and jeweller, and was founded in 1874 by Georges Piaget.
The price of its goods can reach several tens of thousands of euros.
Piaget is part of the Richemont group, which also owns Cartier, Baume and Mercier, Chloe, and Van Cleef and Arpels.
Bulgari and Chaumet stores have also been robbed in recent years.