About 15 men attacked the two vans around midnight Tuesday on the A6 highway at the Avallon tollbooth in the Yonne department, about 170 kilometers (105 miles) southeast of Paris, a police spokesman told CNN.
The spokesman didn't confirm the total value of the jewels taken.
But CNN French affiliate BFMTV reported that the haul was estimated at 9 million euros ($9.5 million.)
The gang used some kind of gas on the van drivers as they commandeered the vehicles, BFMTV said. No shots were fired, said the police spokesman, adding that there were four drivers -- two in each van.
The drivers were being questioned by the Central Office for the Fight against Organized Crime, which is leading the investigation, he said.
The robbers fled in four high-speed cars and the two vans, which were found abandoned -- and emptied of their contents -- near the tollbooth. The burned-out vans have since been taken to a nearby town for examination, the police spokesman said.
A mechanical digger was found with its arm inside one of the vans, he said.
The vehicles of the attackers were spotted driving about 50 kilometers (31 miles) from Avallon toward Paris at some point, police said.
The national police force is using aircraft to hunt for the robbers. Forensic officers are also combing the scene of the crime for clues, BFMTV reported.
The Paris prosecutor's office is in charge of the judicial inquiry.
It's not the first time thieves have targeted high-value jewelry in France.
In one raid in Cannes in July 2013, an armed man made off with jewels worth close to $136 million
, according to the Nice prosecutor's office.
That robbery followed two major jewel heists
during the Cannes Film Festival in May.