The theft is believed to be the biggest such cash heist in France since notorious robber Toni Musulin made off with €11.6 million in 2009.
The vehicle was attacked by several armed individuals as it came out of a branch of the Bank of France in Lyon.
No-one was injured in the attack on the vehicle belonging to the Loomis security company “but the losses amount to €9 million”, prosecutors said in a statement to AFP.
“The perpetrators managed to immediately flee after committing the act.”
Local reports said two vans blocked in the armoured vehicle, one in front and one behind.
The robbers threatened the driver, took the money, and fled in two vehicles later found burnt.
“It was an audacious attack, right in the city centre,” Loomis chief executive Michel Tresch told AFP.
“The most important thing is that the cash escorts are safe and sound,” he added.
The three employees were shocked, Loomis trade unionist Kader Bengueche said, adding they would see a psychologist on Monday.
Cash handling Swedish company Loomis has been attacked several times over the years.
In May 2017, €35 million worth of goods – cash,
diamonds and gold ingots – were stolen from one of its vehicles in Switzerland.
And in December 2016, thieves stole 70 kilos of gold power worth €2.5 million from the same company near Lyon.
But Loomis chief executive told AFP that compared to the 2000s, there were fewer physical attacks today.
“It is a lot easier to carry out attacks (on the internet) via hackers, as opposed to attacking an armoured vehicle,” Tresch said.
“It's not the same exposure.”