Seven paintings by modern masters were brazenly stolen from Rotterdam's Kunsthal Museum in a pre-dawn heist on Tuesday. The massive take is valued at about €309m, and the artworks may be headed to a criminal underground as collateral or held as ransom.

Among the missing are Gauguin's Girl in Front of Open Window; Picasso's 1971 Harlequin Head; Lucian Freud's Woman with Eyes Closed; Matisse's Reading Girl in White and Yellow; Monet's Waterloo Bridge, London, and Charing Cross Bridge, London; and Meyer De Haan's Self-Portrait.

The Kunsthal was showing the works in a special exhibition to mark its 20th anniversary, titled "Avant-Gardes." The exhibition was scheduled to run through January 20 and consisted of 150 works in all from the Triton Foundation Collection, owned by the Cordia family, one of the wealthiest families in the Netherlands.

Family head Willem Cordia, an oil-shipping-textile magnate, built a stunning private collection of 250 artworks over the course of 20 years.

An alarm was triggered at the museum, but the thieves were gone before police arrived just five minutes later.

Art theft losses come to about $6 billion per year, reports the FBI.