AMSTERDAM – Thieves broke into a Rotterdam museum on Tuesday and walked off with works from the likes of Picasso, Monet, Gauguin and Matisse potentially worth hundreds of millions.

Police haven’t said how they pulled off the early hours heist, but an expert who tracks stolen art said the robbers clearly knew what they were after.

“Those thieves got one hell of a haul,” said Chris Marinello, who directs the Art Loss Register.

The heist at the Kunsthal museum is one of the largest in years in the Netherlands, and is a stunning blow for the private Triton Foundation collection, which was being exhibited publicly as a group for the first time.

“It’s every museum director’s worst nightmare,” said Kunsthal director Emily Ansenk, who had been in Istanbul on business but returned immediately.

News of the theft “struck like a bomb,” she said at a press conference in the museum’s cafe.

She declined to reveal any details of how the thieves got in and out with the paintings.

Willem van Hassel, the museum’s chairman, said its security systems are automated, and do not use guards on site.

Police arrived at the scene five minutes after an alarm was triggered, he said.

The collection was on display as part of celebrations surrounding the museum’s 20th anniversary.

The workds included: Pablo Picasso’s 1971 “Harlequin’s Head”; Claude Monet’s 1901 “Waterloo Bridge, London” and “Charing Cross Bridge, London”; Henri Matisse’s 1919 “Reading Girl in White and Yellow”; Paul Gauguin’s 1898 “Girl in Front of Open Window”; Meyer de Haan’s “Self-Portrait,” around 1890; and Lucian Freud’s 2002 work “Woman with Eyes Closed.”

Marinello said the thieves have limited options. They may try to seek a ransom from the owners, the museum or the insurers. They could also conceivably sell the paintings in the criminal market — but only for a fraction of their true worth.