Two men wearing balaclavas and gloves entered the Peninsula hotel, just a stone's throw from the Arc de Triomphe, shortly after midnight and held employees at gunpoint, police sources said.
One of the attackers then used an axe to break into four display cases, making off with items worth a total of €350,000 to €400,000.
An accomplice then drove them away in a car that was found burning shortly afterwards in the suburb of Neuilly-sur-Seine, west of the capital.
No shots were fired and no one was injured in the robbery, the sources said.
France's organised crime brigade has taken over the inquiry.
Luxury Paris hotels have been the target of several robberies in recent years, as have jewellery stores and wealthy tourists visiting the city.
In January 2018, three men were charged over an audacious yet unsuccessful jewellery heist at the Ritz, after they were thwarted by locked doors as they tried to flee.
Last September, three Russian tourists were robbed of thousands of dollars' worth of jewelry and luxury clothing shortly after landing at a Paris airport reserved for private jets.