Paris: Police were hunting more than a dozen armed men who stole millions of euros worth of jewels from two high-security trucks on a motorway south of Paris, a French police official said.

About 15 "heavily armed and battle-hardened" masked men attacked two armoured vans carrying jewels overnight on a highway connecting Paris and Lyon, stealing gems and art worth €9 million ($12.54 million) before vanishing, the police said on Wednesday.

The thieves arrived in four cars and surrounded the vans on the A6 motorway in Burgundy about 200 kilometres south-east of Paris.

"The group carried out the attack around midnight," said police spokesman Cristophe Crepin, adding that the robbers had forced the drivers out, emptied the vans, and then set them on fire a short distance from the toll booth. No one was injured.