Gendarmes and other authorities are combing the Burgundy region southeast of Paris for the attackers, after the latest in a string of big jewel heists in France in recent years.
No one was injured in the attack on the A6 highway connecting Paris and Lyon, and the drivers of the two vans were left at the scene unharmed, a police official said.
The perpetrators escaped in four cars and the two vans, which police found burned and abandoned in a forest near the site of the attack, the official said. The jewels remain missing.
In November, two gunmen robbed a Cartier jewelry boutique in a tony and tourist-filled Paris neighborhood, fled police in a chase across the Seine River, took a hostage - and then surrendered.
In 2013, the Cannes Film Festival was hit by two high-profile thefts. First, a gunman walked into a jewel show at the Carlton International Hotel, stole USD 136 million in loot, and disappeared down a side street. Then, two armed men made off with a haul of luxury watches on the same promenade.