Works by Matisse, Picasso and three other modern masters stolen from a Paris gallery, as it emerged an alarm was out of order at the time of the heist.
The burglar sheared off a gate padlock and broke a window to get into the Musee d'Art Moderne before carrying out the brazen night-time operation. The paintings were found to be missing just as the museum prepared to open.
The major tourist attraction near the Eiffel Tower was sealed off as police sought clues to who was behind the latest stunning robbery that raised new questions about museum security in the French capital.
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Art worth '100 million euros'
"According to estimates by the management of the Musee d'Art Moderne, the value of the stolen canvases totals between 90 and 100 million euros," said a spokesman for Paris city hall, which operates the museum.
Besides the Henri Matisse and the Pablo Picasso, a work by Georges Braque, one by Ferdinand Leger and another by Amedeo Modigliani were plucked from the walls of the city-run museum, one of the most-visited in Paris.
The stolen Picasso alone -- the cubist "Dove with Green Peas," which the Spanish artist created in 1912 -- is worth some 25 million euros, according to the mayor's deputy for culture, Christophe Girard.
The others were French contemporary Matisse's "Pastoral" from 1905, Braque's "Olive Tree near Estaque", Modigliani's "Woman with a Fan" and Leger's "Still Life with Candlestick".
All but the Modigliano were hung in the same room.
Value revised down
Police and judicial sources earlier said the haul was worth 500 million euros (617 million dollars), but art experts said this was unlikely.
"The Picasso might be worth 40 to 50 million euros, the Braque 10 to 20," said Didier Rykner, editor of the specialist magazine The Art Tribune.
"But in any case, we're talking about a theoretical value, they don't have a market value, because you couldn't openly sell them. They're too well known."
Video surveillance cameras recorded only one person entering through a window. Police gave few other details of what happened, although the city spokesman said an alarm system had been over-ridden.
'Partly malfunctioning alarm'
Paris mayor Bertrand Delanoe later said one of the museum's alarms had been "partly malfunctioning" since the end of March, and that it was still awaiting repair when the thieves struck.
Delanoe expressed shock at the theft which he called "an intolerable attack on the universal cultural heritage in Paris."
"This looks like an operation by a professional gang, by organised criminals," said Girard. "We are dealing with an extremely high level of sophistication."
Three security guards on duty
He said the thief managed to slip past three nightwatchmen on duty.
"To get into the museum so fast by disassembling a window, choose five specific works and then slip out unnoticed by the guards, that is quite impressive."
The burglary is the biggest since four paintings by Cezanne, Degas, Van Gogh and Monet valued at more than 180 million Swiss francs (127 million euros, 162 million dollars) were stolen from a Zurich museum in February 2008.
France has seen a growing number of art thefts in recent months.
In January, about 30 paintings -- including some by Picasso and Henri 'Douanier' Rousseau -- were stolen from a private villa in the Cote d'Azur, with a total estimated value of around one million euros.
On New Year's Eve, a pastel by Edgar Degas disappeared from the Cantini museum in Marseille, also in the south of France. The 1877 painting worth 800,000 euros had been lent for an exhibition by the Musee d'Orsay in Paris.
Recovery of stolen works rare
In June last year, the Picasso Museum in Paris was robbed in broad daylight of a book of drawings by the celebrated 20th century artist, worth an estimated three million euros.
Stolen masterpieces are rarely recovered, but three men are being tried in France for the 2007 theft of three Picassos worth more than 50 million euros from the Paris home of his grand-daughter Diana Widmaier-Picasso.
The paintings were found after a five-month investigation.
Located in the well-heeled 16th arrondissement or district in leafy western Paris, the Musee d'Art Moderne is operated by the city authorities and is home to more than 8,000 20th-century works of art.
