WWI UB-45 submarine
An intact German World War I submarine containing 23 bodies was found off the Belgian coast on 19 SeptemberWikimedia Commons

An intact German World War I submarine with 23 bodies inside has been found in the North Sea, according to authorities.

Divers discovered the submarine on the floor of the North Sea, not far from the Belgian coast, on Tuesday (19 September). More than twenty bodies were found on board the vessel.

The Governor of West Flanders, Carl Decaluwe, described the discovery as "very unique".

"It's quite amazing that we found something like this," he said. "The impact damage was at the front, but the submarine remains closed and there are 23 people still onboard."

The submarine is a UB-11, a type of vessel used by the German navy during World War I to disrupt British trade routes. It is 27m long and 6m wide wide, and is lying at an angle of 45 degrees almost 30m below the surface.

Researchers said that damage to the front of the submarine indicates that its upper deck may have struck an underwater mine.

A total of 93 German U-boats were stationed off the Belgian coast and formed a key part of the country's tactics, downing more than 2,500 ships. Seventy of the submarines were lost at sea, killing more than 1,200 sailors during the war.

Only 11 wrecks have been located and authorities say this week's discovery is "the best preserved example".

Belgium's North Sea Minister Philippe de Backer is reviewing whether the submarine will be recognised as a heritage site.