PARIS, France (AFP) -- A lone thief broke into a major Paris gallery and made off with a $120-million haul of modern masterpieces, including works by Matisse and Picasso, officials said yesterday.

The thief sheared off a gate padlock and broke a window to get into the Musee d'Art Moderne before carrying out the brazen night-time heist. The paintings were found to be missing just before the museum was to open yesterday.

Paris mayor Bertrand Delanoe said that one of the museum's alarms had been malfunctioning since the end of March, and that it was still awaiting repair when the thieves struck.

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.

"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.

Police and judicial sources had 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.

Besides the Henri Matisse and the Pablo Picasso, works by Georges Braque, Ferdinand Leger and Amedeo Modigliani were also plucked from the walls of the city-run museum, one of the most-visited in the French capital.

The stolen paintings included Picasso's cubist Dove with Green Peas, which the Spanish artist created in 1912, and his French contemporary Matisse's "Pastoral" from 1905.

The others were Braque's Olive Tree near Estaque, Modigliani's Woman with a Fan and Leger's Still Life with Candlestick.

Delanoe expressed shock at the theft which he called "an intolerable attack on the universal cultural heritage in Paris".