Robbers tunnelled their way into the vault of a Parisian bank at the weekend and cracked almost 200 private safes, police said.
The gang tied up the security guard at a Credit Lyonnais branch on Paris's Avenue de l'Opera on Saturday night, before digging through a series of cellars to reach the vault, police said.
They spent several hours opening the safes and set the place on fire as they left.
The value of the stolen goods is still being estimated, police said.
French media were quick to compare the case to the "Spaggiari Affair", a heist masterminded by Albert Spaggiari more than 30 years ago in Nice.
Spaggiari's gang dug into the vault of a Societe Generale branch, spent two days and two nights there and made away with spoils worth some €24 million.
Reuters