PARIS — In one of the most audacious art heists in decades, thieves wearing balaclavas broke into Paris’ Louvre Museum on Sunday morning, using a crane to smash an upstairs window before stealing priceless crown jewels and escaping on motorbikes, officials said.

The robbery took place at around 9:30 a.m. (0730 GMT) in the Galerie d’Apollon, home to France’s crown jewels, shortly after the museum had opened to visitors, Paris Prosecutor Laure Beccuau said on BFM TV.

“The theft committed at the Louvre is an attack on a heritage that we cherish because it is our History,” French President Emmanuel Macron said on X. “We will recover the works, and the perpetrators will be brought to justice.”

Beccuau said the operation, carried out by four unarmed individuals, lasted only six to seven minutes. The thieves threatened security guards with angle grinders before fleeing with eight of nine targeted objects. During the escape, they dropped one item — the crown of Empress Eugénie, wife of Napoleon III, into the street.

“It’s worth several tens of millions of euros just this crown. And it’s not, in my opinion, the most important item,” said Alexandre Giquello, president of the Drouot auction house.

Beccuau added that it remains unclear why the thieves did not steal the Regent Diamond, one of the museum’s most valuable pieces, estimated by Sotheby’s at over $60 million. “I don’t have an explanation,” she said. “It’ll only be when they’re in custody and face investigators that we’ll know what type of order they had and why they didn’t target that window.”

One of the suspects was reportedly wearing a yellow reflective vest, later recovered by investigators. The group also attempted to set fire to the crane mounted on their truck before escaping, Beccuau said.

Interior Minister Laurent Nunez announced that the investigation had been assigned to a specialized police unit known for solving major art and jewelry thefts. “We’re looking at the hypothesis of organized crime,” Beccuau said, suggesting that the robbery may have been commissioned by a private collector or linked to criminal money laundering. “Nowadays, anything can be linked to drug trafficking, given the significant sums of money obtained from drug trafficking.”

The Louvre, the world’s most-visited museum, said on X that it would remain closed for the day for “exceptional reasons.”

Joan and Jim Carpenter, tourists from California, said they were escorted out of a gallery just before viewing the Mona Lisa. “Well, when you rob the Louvre, that’s a big deal to all of France, so I knew something was up because of the way they swept the whole museum,” Joan Carpenter told Reuters.

The Mona Lisa itself was stolen from the Louvre in 1911 in a heist carried out by a former employee. The painting was recovered two years later, becoming one of the most famous thefts in art history.

Earlier this year, Louvre officials sought government funding to restore its aging halls and bolster security for its vast collection. Macron said a new security plan for the museum, announced in January, “provides for strengthened security.”

Culture Minister Rachida Dati said the robbery underscores the need for modernized protection measures. “For 40 years, there was little focus on securing these major museums, and two years ago, the president of the Louvre requested a security audit from the police prefect,” Dati said. “Why? Because museums must adapt to new forms of crime. Today, it’s organized crime professionals.”