Completed in 1642, the painting, which measures 3.8m x 4.5m and weighs 337kg, 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 newspaper “Nederlands Dagblad”.

“Now it’s striking just how big it is,” he added.

Over a period of three months “The Night Watch” will be put onto 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 usually on display – the “Gallery of Honour”, which 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. The image is available to the public on the Rijksmuseum’s website.