PARIS and LONDON — Several people disguised as construction workers broke into the world-famous Louvre museum in Paris on Sunday, cracking open display cases and stealing jewelry that once belonged to Emperor Napoleon and his wife, officials said.

At least nine pieces of jewelry of “inestimable heritage and historical value” — including crowns, necklaces, earrings and brooches — were taken in the brazen heist before the thieves made their getaway on motorcycles, two ministers said.

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

The French Ministry of Culture later on Sunday released a list of eight items that they said had been stolen, which included two brooches, two diadems, two necklaces and two pairs of earrings.

French President Emmanuel Macron vowed in a social media post that the stolen jewelry will be recovered.

“The theft committed at the Louvre is an attack on a heritage that we cherish because it is our history,” Macron said. “We will recover the works, and the perpetrators will be brought to justice. Everything is being done, everywhere, to achieve this, under the leadership of the Paris prosecutor’s office.” 

Four thieves pulled off the apparently well-planned heist, according to authorities.

The theft took place around 9:30 a.m. local time on Sunday, just before the museum was set to open to the public, the Paris Police Prefecture said in a statement.

The team of thieves drove up to the side of the museum in what police described as a “mobile freight elevator” equipped with a metal ladder on the back that was extended up to a window, according to the Paris police.

“They deployed the freight elevator, securing the surroundings with construction cones, before accessing the second floor, in the Apollo gallery, by breaking the window with an angle grinder,” according to the police statement. “Inside, they then smashed two display cases, ‘Napoleon jewels’ and ‘French crown jewels,’ using the angle grinder and stole numerous pieces of high-value jewelry.” 

Two of the thieves arrived at the museum in the mobile freight elevator, one wearing a yellow vest and the other an orange vest, according to police. Two accomplices arrived at the museum at the same time on what police described as “T-max vehicles” or sports motorbikes.  

“The staff on site, upon seeing what was happening, took to safety,” according to the police statement. “An alarm was triggered at 9:37 a.m. The perpetrators exited through the window by going back down the freight elevator before fleeing on the two motorbikes at 9:38 a.m.”

The Paris Prosecutor’s Office said the perpetrators tried and failed to set fire to the mobile freight elevator they used in the heist before they fled the scene.

Police say they’re investigating a video obtained by BFMTV, a French news broadcast television and radio network, which they believe shows one of the suspects appearing to try to access one of the jewelry cases.

Following the heist, police found two angle grinders, a blowtorch, gasoline, gloves, a walkie-talkie, a blanket, and a crown at the scene. Police also found a yellow vest that was apparently dropped by one of the fleeing perpetrators at the corner of Pont de Sully and Avenue Henri IV, several blocks from the Louvre, police said.

French Interior Minister Laurent Nunez, in an interview on local radio, said the value of the items would be “inestimable.”

According to the French Ministry of Culture, among the items stolen was a diadem, or crown, from the collection of Queen Marie-Amelie and Queen Hortense; an emerald necklace and a pair of emerald earrings from the collection of Marie-Louise, Napoleon’s second wife; and a large bow brooch from Empress Eugenie’s bodice.

The thieves either dropped or abandoned two pieces of jewelry as they exited the museum, including one of Empress Eugénie’s crowns, according to the Paris Prosecutor’s Office, which said it is investigating the case as an aggravated theft by an organized gang and criminal conspiracy to commit a crime. 

The alleged robbery took less than seven minutes, he said.

A notification posted on the Louvre’s website shortly afterward said, “The Louvre Museum will remain closed today for exceptional reasons. We thank you for your understanding.”

The decision to close the museum was made jointly by its management, the police and the Ministry of the Interior, museum officials said in a statement. The doors were closed as “a security measure and to preserve traces and evidence for the investigation,” the statement said.

Kaci Benedetti, who was visiting Paris from the United States, told ABC News she was standing in line to enter the museum on Sunday when a commotion began. Police were running along the courtyard where Benedetti and her family were waiting, she said.

She watched as the officers attempted to enter the building through a side door, but “could not because they were locked,” she said.

“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 news of the robbery came first from French Minister of Culture Rachida Dati, who said on social media, “A robbery took place this morning at the opening of the Louvre Museum.”

Dati added, “No injuries to report. I am on site alongside the museum teams and the police. Investigations underway.”

Christopher Marinello, the CEO and founder of Art Recovery International, told ABC News that security at the Louvre is known as “the best in the world.”

“So this is a very audacious crime and a slap in the face to museums everywhere,” Marinello said, adding that investigators are now “in a race against time” to recover the stolen jewelry before the thieves attempt to sell the items to buyers who likely will not purchase the pieces intact.

“The criminals are going to try to hide what they have just done and the way they hide it is by breaking up those jewels, by recutting those stones, by melting down the precious metals,” Marinello said. “They are now doing that. And the police have a very short window to locate these thieves and try to recover these items.”

Nathalie Abbou Vidal has spent her life surrounded by jewels that have lived through revolutions, crowned emperors and survived wars. As one of France’s leading jewelry historians, she teaches at the prestigious Haute Ecole de Joaillerie and advises major auction houses and the French courts.

She told ABC News the idea that these treasures — “too important, too full of history, too much a part of who we are” — could be dismantled for profit is almost unthinkable.

“The weight of the gold is nothing. The diamonds — they’re old European stones, centuries old. You can’t just break them apart,” she said.

Even the black market, she believes, will struggle to erase the identity of the pieces. “They’re not just objects. They’re part of our heritage.”

ABC News’ Victoria Beaule contributed to this report.