It was the French Collection.

A trio of slick robbers disguised as construction workers took less than 10 minutes to break into the Louvre Museum in front of visitors and workers Sunday and coolly make off with millions of dollars in gems, French authorities said.

Here’s how the sensational, lightning-quick heist went down.

At 9:30 a.m., just half an hour after the famed art museum opened, the gang of three thieves arrived at the central Paris tourist attraction on scooters.

They then used a basket lift to get up to a second-floor window and wielded gas-powered mini chainsaws to break in, Le Parisien reported.

The masked and hooded crooks had placed the basket lift at the museum themselves and “threatened the guards who were present at the scene,” Paris prosecutor Laure Beccuau told BFMTV.

“We have CCTV footage from the museum itself,” she said, adding that evidence so far points to a high degree of “preparation and organization” from the thieves — who pulled off their caper in less than 600 seconds.

Dramatic video from inside the Louvre shows one of the criminals, wearing a green reflective vest typical of those found at construction sites, calmly cutting through a glass case surrounding one of the targeted items as visitors watched.

A Stihl Cutquick concrete saw, which retails for $1,300, was used to gain access to the cases.

Footage of the theft shows two of the masked robbers entering “calmly” and smashing display cases containing French crown jewels worth an “incalculable” amount of money, officials said.

“No violence, very professional,” said France’s culture minister, Rachida Dati, to TF1, describing the thieves as appearing to be highly “experienced.”

The theft took place just 270 yards from the Mona Lisa and saw nine of France’s most valuable pieces of jewelry snatched.

By 9:40 a.m., the two robbers had left the building through the same window and got to the ground thanks to the spider lift, where the third crook was waiting.

They all then got onto scooters and fled, although in their rush to escape, they left behind several key pieces of evidence, French authorities said.

One of the stolen objects, an emerald-set imperial crown containing more than 1,300 diamonds that once belonged to Napoleon III’s wife, Empress Eugenie, was found broken outside the museum, Le Parisien reported.

Police arrived minutes later to also find the spider lift, the concrete saw, a yellow reflective jacket used by another one of the thieves, a blowtorch, two angle grinders, gloves, gasoline and a blanket, the outlet said.

The robbers were last seen in security video riding away on their scooters heading southeast out of central Paris toward the A6 highway.

Thousands of baffled visitors were soon evacuated from the museum, which was shut for the rest of the day.

Forensic teams were pictured taking samples around a broken window on the south side of the building facing the River Seine, where construction work was taking place.

No information has yet been released on the identities of the thieves, nor has it been ruled out that they were foreign nationals, Beccuau said, adding that the  heist was most likely the work of “organized crime.”

French President Emmanuel Macron vowed that the jewels and the robbers would be found.

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

“Everything is being done, everywhere, to achieve this, under the leadership of the Paris prosecutor’s office,” he added.

The stolen items include a diamond and sapphire tiara that belonged to the last queen of France, Maria Amalia, as well as to Queen Hortense, the daughter of Napoleon Bonaparte’s first wife, Josephine.

A sapphire necklace and earrings from the second collection are also missing, as well as an emerald necklace and earrings that belonged to Marie-Louise, Napoleon’s second wife.

Also reportedly gone are a reliquary brooch, which is designed to hold a religious relic, a tiara and a bodice knot belonging to Empress Eugenie.

Remarkably, a 140-carat diamond known as “the Regent,” the centerpiece of the collection, was untouched by the robbers.

The Apollo Gallery was previously raided in 1976, when armed robbers stole a sword that once belonged to King Charles X.

The sword was never recovered, with experts speculating that it was quickly melted down by the thieves.

The Louvre is the world’s most popular art museum, with almost 9 million visitors in 2024 alone.

With Post wires