Rembrandt van Rijn's masterpiece The Night Watch was taken down and removed from its frame in the Netherlands' national museum on Wednesday for the first time since 1975.

The painting measures 3.8 meters by 4.5 meters and weighs 337 kilograms. It was completed in 1642 and portrays the captain of an Amsterdam city militia ordering his men into action.

"For the first time in almost 50 years, The Night Watch is flat on its belly," Rijksmuseum Director Taco Dibbits told Dutch newspaper Nederlands Dagblad. "Now it's striking just how big it is."

Over a period of three months the painting will be put on to a new aluminium frame, which will remove some warping of the canvas.

The restoration is being done behind glass walls in the gallery where the painting is normally on display. The museum's "Gallery of Honor" shows works by Dutch painters of the 17th century, known as the country's Golden Age.

As part of the restoration project, the painting has recently been photographed to create an ultra high-resolution digital version, which the museum says is the most detailed photo ever taken of a work of art.