The hold-up, which resembles the plot of a Hollywood action movie, took place on Thursday near the French-Swiss border.
It began in the evening in the southeastern French city of Lyon, where two men pretending to be plumbers kidnapped a young woman from her apartment, a source close to the investigation told AFP.
They bundled her into a car and then had accomplices ring her father, who works for a Swiss company that transports money between companies and banks, to demand a ransom.
The father, who lives in the French border town of Annemasse, was carrying out a cash delivery when the call came through, Europe 1 radio reported.
He agreed to meet the kidnappers in a car park just across the border on the Swiss side, to hand over the van's contents, investigators said.
Police in the Swiss canton of Vaud said that the father was en route to Lausanne when he was forced to exit the motorway and head for the car park where he was met by robbers wearing gloves and balaclavas.
Daughter found by roadside
"There, several armed men who were awaiting the van made him park it. They then held up the delivery drivers, completely emptied the van's contents and fled in a dark-coloured Porsche SUV," the Swiss police said in a statement on Friday.
A French police source told AFP that the van was carrying "between 20 and 30 million Swiss francs (17-26 million euros, $21-32 million)".
A spokesman for the police in Vaud refused to confirm the amount.
The driver's daughter, who is in her twenties, was found unharmed at around 10pm on a road on the outskirts of Lyon.
She was questioned by police on Friday and said to be still in a state of shock.
"We have no reason to question her story," a French source with knowledge of the investigation said, adding that police suspected a criminal gang.
No arrests have been made yet in the probe, which is being led by French police.
Swiss police said they were looking for three men with accented French, "maybe from the south of France or North Africa" and called on any witnesses to come forward.
"Many details remain unexplained," the French source said, adding that the investigation was expected to take some time.