Thieves in balaclavas broke into Paris’ Louvre, the world’s most-visited museum, and stole priceless objects from an area that houses the French crown jewels before escaping on motorbikes, officials said.

The thieves pulled up outside the Louvre on Sunday morning, on a road along the Seine river, and climbed an extendable ladder to break into an upper window that looks into the Galerie d’Apollon, or Apollo Gallery, authorities said.

The thieves struck at about 9:30 am when the museum had already opened its doors to the public, and entered the Galerie d’Apollon building, Paris Prosecutor Laure Beccuau said on BFM TV.

The robbery took between six to seven minutes and was carried out by four people who were unarmed, but who threatened the guards with angle grinders, she said.

A total of nine objects were targeted by the criminals, and eight were actually stolen. The thieves lost the ninth one, the crown of Napoleon III’s wife, Empress Eugenie, during their escape, Beccuau said.

Jewels stolen

The Culture Ministry said the following eight pieces were stolen.

The crown of Empress Eugenie was found outside the museum. The thieves apparently dropped the piece, made of gold, emerald and diamonds, as they made their getaway.