Seven paintings, including several by modern masters Pablo Picasso, Henri Matisse, and Claude Monet were stolen from Rotterdam's Kunsthal museum early Tuesday around 3 a.m. local time (9 p.m. Monday ET).
Also stolen were works by Lucian Freud, Paul Gauguin, and Meyer de Haan.
The heist, one of the largest in years in the Netherlands, occurred while the private Triton Foundation collection was being exhibited publicly as a group for the first time. The collection was on display as part of celebrations surrounding the Kunsthal's 20th anniversary celebrations.
Neither the police nor the Kunsthal were immediately able to put a value on the haul, but the theft is one of the art world's most dramatic in recent years and will likely be worth millions.
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Kunsthal, designed by Dutch architect Rem Koolhaas, does not have its own collection and exhibits different types of art, including photos, sculptures, design and fashion.
The museum was closed Tuesday as police reviewed videotape footage and called on witnesses to come forward.