Five paintings, including a Matisse and a Picasso, were stolen overnight from Paris' Musee d'Art Moderne.
The theft included works by Georges Braque, Ferdinand Leger and Amedeo Modigliani, French police said.
The artworks are worth a total of just less than 100 million euros ($123.7 million), said Christophe Girard, cultural attache to the Paris town hall, which runs the museum.