Several paintings by famed artists were stolen from a museum in the Netherlands in the wee hours of the morning on Tuesday.

Seven pieces of art were stolen from the Triton Foundation Collection at the Kunsthal museum in Rotterdam, including pieces by Picasso, Matisse and Monet. The heist is being considered one of the largest to occur in the Netherlands in many years.

According to the New York Daily News, the stolen works were Picasso's 1971 "Harlequin Head"; 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."

Kunsthal spokeswoman Mariette Maaskant says that the paintings were of “considerable value.” however, independent experts told the Daily News that the works “were clearly worth millions of dollars but would be impossible to sell on the open market.”

The theft took place around 3 a.m. local time, according to CNN. The museum’s alarms alerted security that discovered the paintings missing and contacted police, who immediately began investigating.

Police report that they are reviewing surveillance videos, speaking to witnesses, and have already collected evidence.

"Initial investigations show the burglar was well prepared," police said in a statement.

They have not divulged any other details, but are reaching out to the public for any other witnesses to come forward.

The Triton Collection from which the paintings were stolen is a private collection that was recently put on display for the first time in honor of Kunsthal’s 20th anniversary. According to CNN, the collection includes over 150 pieces dated from the "late nineteenth century to the present day” that were collected over 20 years.