The robbers, wearing masks and jumpsuits, burst into the museum during opening hours, armed with handguns and threatened staff members before they took the four paintings, put them into bags, and then escaped. Two of them fled on a motorcycle, while the three others escaped by car.

The four stolen works are valued at about $1.4 million, police said. Two of the works by Impressionist painters, Claude Monet and Alfred Sisley, had already been stolen once in 1998 but were recovered a week later on  a boat in a nearby town, Monique Bailet, assistant curator of the museum said. The museum's curator at that time, Jean Fornéris, was convicted for that heist and sentenced to five years in jail.

The stolen oil paintings include Falaises près de Dieppe painted by Monet in 1897 and Sisley's Allée de peupliers de Moret dating back to 1980. The Sisley painting had been stolen in 1978 while on loan for an exhibition in Marseilles but was recovered a few days later in the same town.  The other paintings, by Brueghel, were Allégorie de l'eau and Allégorie de la terre.

Built in 1878, this magnificent private mansion houses a collection of more than 6,000 works of art dating from the 17th century to the 1940's. As well as work by French artists (including sculptures by Carpeaux and Rodin), the museum also boasts a fine collection of remarkably restored Flemish school paintings. Two exhibition spaces are entirely devoted to modern art, featuring Kees Van Dongen, Raoul Dufy and Picasso. Of particular note is symbolist work by Nice artist Gustav Adolf Mossa.