The convoy was heading through northern Paris on its way to Le Bourget airport late on Sunday evening when it was raided, reports say.
The gunmen seized a vehicle carrying the money and documents, later releasing the driver and two others.
The convoy was said to have come from the Saudi embassy. No-one was hurt.
The gunmen, reportedly armed with Kalashnikov rifles, targeted a Mercedes mini-van at 21:15 (19:15 GMT) on the northern ring road, or peripherique, at Porte de la Chapelle, on the edge of Paris.
The motorcade, belonging to a Saudi prince, was ambushed by eight people in two separate vehicles who pointed their guns at the driver of the Mercedes, forcing him to stop, French media reported.
The men then drove the vehicle away with the driver and the two other Saudis inside. No shots were fired but the Saudis were later freed.
"In the vehicle there was roughly 250,000 euros in cash and official documents from the embassy," police union spokesman Rocco Contento told BFM TV news.
According to Contento, the operation lasted just a few seconds, something that pointed to "a very organised and especially informed commando unit, who had information and accomplices".
"As far as I am concerned, it looks very much like it could be commandos from eastern Europe, who we know about, who are often paid to do dirty work."
The Mercedes was heading to Le Bourget airport with paperwork for the departing prince, who has not been named, according to the prosecutor's office. Le Bourget is often used for high-level visitors taking private jets to Paris.
The vehicle was eventually found abandoned and another of the gang's cars was found burned out.

The Channel 4 celebrity winter sports competition ended last night with a showdown between the Made in Chelsea star and Olympic gymnast Louis Smith.
Spencer came out on top to win the cow bell trophy as he beat  Louis Smith by almost one metre in the final jump.
The Made in Chelsea star told fans 'To all those who supported me in #TheJump thank you from the bottom of my heart. Love to all my fellow competitors too!!'

The MSP will make the pledge in her keynote address to the Scottish Labour conference in Perth.
Ms Dugdale believes new taxes would not be necessary to pay for the plan.
She will advocate changes of approach such as ditching SNP plans to cut air passenger duty and Tory proposals to raise higher rate tax thresholds.
Ms Dugdale will say that parties in Scotland must "get serious" about what they would do with the major new tax and welfare powers coming to the Scottish Parliament.
The MSP reckons the restoration of tax credits could be achieved by making different choices in government.
At the Holyrood election in May next year, the Scottish Labour Party will be defending the 38 seats it holds.
Ms Dugdale will tell her conference that a vote for her party would offer a break from Tory austerity.
She will add: "Scottish Labour will stand for the elections with a promise to restore the money Scottish families will lose from this Tory tax rise on working families.
"We will act as soon as the new powers make it possible. We don't need to tax ordinary Scots more to make this change.
"We just need to make different choices from the Tories and the SNP."
The Scotland Bill, currently going through the UK parliament, will contain new powers for Holyrood, including;
On the first day of the three-day conference Labour's UK leader Jeremy Corbyn urged voters in Scotland to back a "left wing alternative" at next May's Holyrood election.
Mr Corbyn also said it was right that decisions about the party north of the border should be taken by members and activists in Scotland.
He has signed an agreement with Ms Dugdale pledging a more autonomous structure.
Who would join Scottish Labour - a party with just one MP north of the border and a poor showing in the polls?
Five young people - attending the Scottish Labour conference in Perth - tell BBC Scotland political reporter Philip Sim (@BBCPhilipSim) what's making them stick and not quit.
Heavily armed men have attacked a convoy of cars belonging to a Saudi prince, stealing 250,000 euros (£200,000; $330,000), police say.
[NEXT_CONCEPT]
The winner of The Jump 2017 is Spencer Matthews.
[NEXT_CONCEPT]
A future Labour government at Holyrood would restore tax credits for working families, its Scottish leader Kezia Dugdale will tell party members.