Those attacked told police a group of eight people stopped the car as it was driving on the Paris city ring road at around 9.30 on Sunday evening.
Some reports say the attackers were armed with Kalashnikovs, though no one was injured in the attack, which took place around the Porte de la Chapelle area, in northern Paris.
The motorcade was making its way from the Saudi embassy to an airport in Le Bourget, where a private jet was waiting.
The thieves drove off in the last car of the motorcade, taking with them the chauffeur, an assistant and a bodyguard.
They were released nearby. The motorcade monospace, as well as another car used by the robbers, were found burnt out on the outskirts of Paris.
No suspects have yet been apprehended.
"It's quite an unusual attack. They were obviously well-informed. It's true that it's quite a rare way of operating," said a police source.
Investigators are trying to find out whether the attackers were interested in the money or the documents they stole, which the French newspaper Le Parisien describes as “sensitive”.