Three or four thieves swiped rings, necklaces and luxury watches from display cases at the Harry Winston store near the Champs-Elysees, a police official said. They brandished handguns and threatened about 15 employees, hitting some on the head with guns, the official said.
At least two of the bandits were men wearing wigs and dressed as women, at times spoke a foreign language, and knew employees' names, the official said. After the theft, the robbers fled.
The official, who was not authorized to be publicly named according to agency policy, said it was among France's biggest-ever jewel thefts.
New York-based Harry Winston said in a statement: "We are cooperating with the authorities in their investigation. Our first concern is the well-being of our employees."
A spokeswoman for the company would not provide further details on the theft. It was unclear whether anyone was injured.
The boutique, on the expensive Avenue Montaigne, was closed to the public Friday. Three of the five display windows stood empty of their usual wares.
The store was targeted in a similar theft in October 2007, when three people forced employees to open safes and hand over euro10 million worth of jewels.
A security monitoring group for the French jewelry industry has reported a 20 percent rise in armed robberies this year over last, with 132 incidents in the first 11 months of 2008.
In London, police have reported a recent rise in holdups of security vans. Police say it could be linked to the credit crunch and predict the trend to continue as Christmas approaches.
Associated Press writer Jamey Keaten contributed to this report.