Masked gunmen snatched four masterpieces Sunday from the Museum of Fine Arts in Nice. The five men dashed in and made off with four paintings worth about .4 million, police said. The stolen paintings were Monet's 1897 Cliffs

Paris ? Five armed, masked thieves sprinted into an art museum on the French Riviera during opening hours Sunday afternoon and snatched a Monet and three other masterpieces off the walls in the latest brazen heist of high-profile art from the rich collections of Europe.

Wearing jumpsuits, the robbers ordered guards to lie on the floor at gunpoint as accomplices fanned through the galleries of Nice’s Museum of Fine Arts. One thief grabbed French impressionist Claude Monet’s “Cliffs Near Dieppe” while others snagged the bucolic “Lane of Poplars at Moret” by another impressionist, Alfred Sisley, and two evocative oil paintings by Flemish Baroque-era artist Pieter Bruegel the Elder, according to Interpol, the international police agency.

The thieves stuffed the artworks in bags and made their getaways by motorcycle and car, French authorities said Monday. Interpol described the haul as “four paintings of inestimable value.”

“Who could expect to be held up in broad daylight like that?” Patricia Grimaud, deputy curator of the museum, said in a telephone interview Monday from Nice. “They were really bold and quick; it took them only 10 minutes. I can’t find the right words to describe what they did.”

The daytime heist of well-known paintings ranks among the most audacious examples of a growing number of thefts from public and private collections, according to French law enforcement officials. Interpol estimates that art thefts total billions of dollars a year, with France and Italy consistently hit hardest because of their vast troves of art and artifacts.

Nice museum officials said Monday that the 1897 Monet and 1890 Sisley paintings had been stolen in a previous incident involving the same museum nine years ago. The Monet was later found in a boat under repair at a marina and the Sisley was recovered in the sewers of Marseilles on France’s southern coast, according to French media reports. The museum curator at the time was convicted of complicity in the thefts and sentenced to five years in prison.

Grimaud, the deputy curator, said Monday that she arrived at the museum in downtown Nice 10 minutes after Sunday’s robbery. “Yesterday the museum was free, like every first Sunday of the month,” she said. “We had six guards for the two floors.”

At 1 p.m., the five armed thieves “held up the two downstairs guards, went upstairs, held up the guards there and took the four paintings off their X-shaped hooks and left,” she said.

The robbers attempted to steal a fifth painting, but it was too large to fit into their bags, according to witnesses cited in French news accounts. About half a dozen visitors were in the museum at the time, authorities said.

The men ran out of the ornate, ocher-colored 19th century villa that houses the museum; two hopped on a motorcycle and the three others leaped into a waiting car and sped away, authorities said.

“We don’t have security devices for each painting,” Grimaud said. “It’s very easy to remove a painting from its hook. The fact that there were few visitors and few guards made it much easier for them.”

Grimaud, who said she was questioned by police for 2 1/2 hours Monday morning, said the museum alarm is turned on only when the museum is closed.

The Monet and Sisley works were on loan to the Nice museum from the Musee d’Orsay in Paris.

Authorities said the oil paintings would be impossible to sell on the open art market.