The Louvre was closed for a second day Monday as police hunted for thieves who broke in and stole priceless royal jewels in a spectacular daylight robbery.

Officials said a team of 60 investigators was working on the theory that an organised crime group was behind the theft Sunday of nine pieces of jewellery, one of which -- a crown covered in more than 1,000 diamonds -- they dropped in the streets of Paris as they fled.

As disappointed tourists rebooked tickets to the world's most visited museum, the heist -- which lasted just seven minutes -- also reignited a row over the lack of security in France's museums, after two other institutions were hit last month.

Justice Minister Gerald Darmanin admitted to flaws in securing the Louvre.

"What is certain is that we have failed, since people were able to park a furniture hoist in the middle of Paris, get people up it in several minutes to grab priceless jewels, giving France a terrible image," he told France Inter radio on Monday. 

Interior Minister Laurent Nunez has ordered better protection measures around cultural sites, his advisers said.

A report by France's Court of Auditors seen by AFP covering 2019 to 2024 points to a "persistent" delay in the museum's security upgrades, with for example just a fourth of one wing of the museum covered by video surveillance. 

The thieves arrived at around 9:30 am (0730 GMT) on Sunday, shortly after the museum opened at 9:00 am, sources and officials said.

They parked a truck with an extendable ladder like those used by movers below the Paris museum's Apollo Gallery, clambering up and using cutting equipment to get in through a window and open the display cases.

The world-famous institution, whose extensive collections include the Mona Lisa, may not open again until Wednesday, as it is usually shut on Tuesdays.

Shortly before the announcement it was staying closed, queues of impatient visitors had snaked their way across the museum's pyramid courtyard and under the tall arches of the main entrance gallery, hoping to get in.

US tourist Jesslyn Ehlers, 38, and her husband were busy rebooking their tickets. 

"We're just kind of disappointed. We've been planning this for a very long time," she said.

Carol Fuchs, an elderly tourist from the United States, had been standing in line for more than three-quarters of an hour.

"The audacity, coming through a window," she told AFP after the disappearance of the jewels.

"Will they ever be found? I doubt it. I think it's long gone," she said.

- Diamonds, sapphires missing -

The masked thieves dropped and damaged the crown of Empress Eugenie, the wife of Napoleon III, as they made their escape. It is covered in 1,354 diamonds and 56 emeralds, according to the museum's website.

But eight priceless items of jewellery remain missing, according to the culture ministry.

The list they released included an emerald-and-diamond necklace that Napoleon I gave his wife, Empress Marie-Louise.

Also stolen was a diadem that once belonged to the Empress Eugenie, which is dotted with nearly 2,000 diamonds, and a necklace that once belonged to Marie-Amelie, the last queen of France. It is adorned with eight sapphires and 631 diamonds, according to the Louvre's website.

The loot would be impossible to sell on in its current state, said Alexandre Giquello, president of the leading auction house Drouot.

The raid -- which saw some 2,000 people evacuated from the museum -- is thought to have been carried out by an experienced team, possibly "foreigners", Nunez has said.

The intervention of museum staff forced the thieves to flee, leaving behind some of the equipment used in the raid, the culture ministry said.

It was the first theft from the Louvre since 1998, when a painting by Camille Corot was stolen and never seen again.

France's museums have previously come under criticism for poor security, with many viewed as being less secure than banks and seemingly increasingly targeted by thieves.

Last month, criminals broke into Paris's Natural History Museum, making off with gold samples worth $700,000.

The same month, thieves stole two dishes and a vase from a museum in the central city of Limoges, the losses estimated at $7.6 million.