The stolen jewels were found in the bag dropped by the thief on the scooter, the sources say, as he collided with a pedestrian.
The men broke a window at the tradesman's entrance to the famed hotel just after 6.30pm (5.30pm United Kingdom time).
Three robbers, armed with axes, carried out the robbery late on Wednesday at the hotel on the city centre's Place Vendome, next to the Justice Ministry. The overall value of the jewels on display was estimated at about $5.4m.
The three men who were arrested are all around 30 years old and are from the Seine-Saint-Denis area north of Paris.
Three robbers were later arrested after being blocked in the building.
The hotel, now owned by Egyptian billionaire Mohammed al-Fayed, first opened in 1898 and was the first Paris hotel to boast electricity on all floors and bathrooms that were inside rooms.
The suspects inside threw bags of goods out of a window to at least two accomplices outside, according to a police official. Two accomplices waiting outside were thrown some of the stolen goods and escaped by auto and motorbike.More news: Pakistan ends intelligence cooperation with U.S. as aid halts — Global Geopolitical Series
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But another two thieves, who waited outside, managed to escape by vehicle and scooter. It was the last place Princess Diana stayed before her fatal auto crash in a Paris tunnel, and hosts elite guests from around the world drawn to the refined neighborhood.
The two accomplices escaped, one in a auto, the other on a motorcycle.
Witnesses at the hotel's Hemingway Bar saw the robbery unfold.
Place Vendome has been the scene of several daring jewellery heists in recent years.
But the audacious strike at one of Paris's most glamorous hotels could cast a cloud over the Ritz's image.
France has found itself repeatedly in the headlines for high-profile robberies, particularly in Paris and on the Cote d'Azur.
Five men held up Kardashian at gunpoint in the luxury apartment where she was staying, making off with a diamond ring and other jewellery pieces valued in total at nine million euros.
In October 2016, reality television celebrity Kim Kardashian was the victim of a robbery just 10 minutes walk from the Ritz, in which millions of dollars' worth of jewellery was stolen from her.