Around 15 armed thieves attacked two vans carrying jewels worth £6.3m on a French motorway, ejected the drivers and drove them away.
Authorities are combing the Yonne region in Burgundy, about 125 miles southeast of Paris, and surrounding areas for the attackers.
The police official says no one was injured in the attack, which took place at around midnight, and the drivers of the two vans were left at the scene unharmed.
The official says the two vans were found burned in a forest near the site of the attack, which happened on the A6 connecting Paris and Lyon. The jewels were not found.
The heist reportedly took place at the Avallon toll both on the motorway.
No possible suspects have been named in Wednesday's theft, although the case was reminiscent of heists by the Pink Panther gang of jewel thieves.
The Pink Panther network has been credited with a series of thefts that Interpol says have netted more than 330 million euros since 1999.
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 $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.
Last month, eight people were convicted in connection with one of the most spectacular jewel thefts in recent French history at a Harry Winston boutique in Paris. In the 2008 hold-up, three cross-dressing gunmen stole about £61 million in goods.
Police have set up a perimeter around the heist with air support, AFP reported.