The robbers managed to elude a high-security surveillance system and burst into the boutique at 1630 GMT on Thursday, during the busy holiday shopping season.
Brandishing weapons, they threatened some of the dozen employees and customers and herded them into a corner.
Investigators said some of the employees had suffered blows.
The haul, initially estimated at up to $79m, was revised early on Friday to $102m, making it France's biggest jewellery heist by far.
Police said they were dealing with "major pros" who had meticulously planned their crime and knew the boutique's lay-out, suggesting it may have been an inside job.
The thieves, who were said to be French-speaking, stuffed brooches, rings, necklaces and other finery into bags and quickly left, without firing a shot.
Detectives said there was a possibility that the robbers may have connections in eastern Europe, where the loot could be sold more easily than in western Europe where such goods would be quickly detected.
Police described the eastern European market as a "new El Dorado for traffickers" trying to get rid of high-end stolen goods.
They were questioning customers, employees and pedestrians on Friday to try to come up with clues.
Harry Winston, which specialises in luxury jewellery for its wealthy international clientele, was hit by another heist in October last year when armed robbers stole an estimated $2.8m worth of valuables.
An insurance company offered a $500,000 reward for information leading to the thieves' arrest but they were never found.
The US jewellery chain has stores across the world and has sold precious stones to royal families and lent them to film stars for events such as the Cannes film festival and the Oscars.
Belgium holds the record for the world's biggest jewellery heist, when diamonds worth $127m or more were stolen on February 14, 2003, in Antwerp.
Among other notable heists, three Paris shops were targeted in October 2001 by a conman posing as a rich Kuwaiti who managed to make off with $2.8m in jewels.