Several people posing as construction workers broke into the world-famous Louvre Museum in Paris on Sunday, smashing display cases and stealing jewelry once owned by Emperor Napoleon and his wife, officials said.

According to authorities, at least nine pieces of jewelry described as having “inestimable heritage and historical value” were taken before the suspects escaped on motorcycles.

The Louvre said the suspects broke a window and entered the Apollo Gallery, which houses the French crown jewels, around 9:30 a.m. local time. The exact details of the stolen items have not yet been released.

“Investigations have begun, and a precise list of the stolen items is underway,” the museum said in a statement.

French Interior Minister Laurent Nunez told local radio that the items’ value was “inestimable” and said at least three suspects appeared to be involved.

He said the thieves used a construction ladder to gain entry and that the entire robbery lasted about seven minutes.

An investigator with the Banditry Repression Brigade, a police unit that handles major robberies and art thefts, said the suspects wore construction uniforms and covered their heads with hoods. The investigator added that two of the thieves entered the gallery while one remained outside, using small chainsaws to cut open the display cases.

Shortly after the break-in, the museum announced on its website:

“The Louvre Museum will remain closed today for exceptional reasons. We thank you for your understanding.”

Kaci Benedetti, a visitor from the United States, told ABC News she was in line to enter the museum when police suddenly rushed across the courtyard.

She said officers tried to get into the building through a side door but couldn’t because it was locked.

“We could see people inside running and some were banging on the glass doors to get out, but could not because they were locked,” Benedetti said. “Then police and military police arrived. After about an hour they announced the Louvre was closed for today.”

The first official confirmation of the robbery came from French Minister of Culture Rachida Dati, who posted on social media:

“A robbery took place this morning at the opening of the Louvre Museum. No injuries to report. I am on site alongside the museum teams and the police. Investigations underway.” (Sunday Tribune)