Police haven't said how the thieves 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.
She declined to reveal any details of how the thieves got in and out with the paintings, or how the museum is protected, other than describing its security as "state of the art" and "functional." 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. He described the museum's insurance as adequate for the exhibition.
Police spokeswoman Willemieke Romijn said investigators were reviewing videotapes of the theft, which took place around 3 a.m.
The Art Loss Register's Marinello said the items taken could be worth "hundreds of millions of euros" if sold legally at auction. However, he said that was now impossible.
They included Pablo Picasso's 1971 "Tete d'arlequin," Henri Matisse's 1919 "Reading Girl in White and Yellow," Claude Monet's 1901 "Waterloo Bridge, London" and "Charing Cross Bridge, London" and Paul Gauguin's 1898 "Girl in Front of Open Window."