The well-preserved wreck of a First World War German submarine, possibly still containing the remains of its 23 crew members, has been found by a marine archeologist off the Belgian coast.

Tomas Termote was diving off Belgium's coast in June when he found the 27-metre-long sub, Belgian officials said this week.

The use of submarines, often referred to as U-boats, in the First World War to disrupt British trade routes in the English Channel and the North Sea was a key part of German tactics.

The 93 German U-boats stationed in Belgian ports sank more than 2,500 ships, but were also a target, with 70 of them lost at sea, killing 1,200 sailors.

Termote said his investigation of the submarine about 27 metres below the surface revealed impact damage at the front, possibly from a mine, but it appeared to be largely intact.

It was not yet clear which of the 11 known wrecks of the German submarines had been found, and authorities said they would not give the exact location of the wreck to deter looters.

"Of the 11 downed U-boats in Belgian waters, this one is the best-preserved example," a statement from the province of West Flanders said.

Carl Decaluwé, governor of West Flanders — who authorized the dives — announced the discovery at a news conference Tuesday.

The wreck was first seen on sonar scans of the sea floor conducted by the Belgian government, but at the time the wreck was thought to be a Second World War landing craft.

Termote told the website Live Science that closer examination of the multibeam sonar scans revealed the distinct shape of the U-boat, "pointed at both ends with a tower in the middle."

Belgium's North Sea minister said he would investigate whether the wreck could be recognized as a heritage site.