Researchers have discovered the world's oldest intact shipwreck in the depths of the Black Sea, where it has lain untouched for over 2,400 years.

The 23-metre vessel is thought to be an ancient Greek trading ship and resembles a design previously only seen on pottery from the era including the "Siren Vase", currently on display in the British Museum.

It was discovered just over a mile beneath the water close to the coast of Bulgaria by the Black Sea Maritime Archaeology Project (MAP), an international group of archaeologists, scientists and marine surveyors.

Researchers said the oxygen-free water had helped to preserve the material.

The team retrieved a small piece of the wreck, which was then carbon dated to confirm its age.

"A ship, surviving intact, from the classical world, lying in over two kilometres of water, is something I would never have believed possible," said Professor Jon Adams, principal investigator for the project.

"This will change our understanding of shipbuilding and seafaring in the ancient world."

The wreck is one of over 60 vessels found by the group in the last three years.

Other discoveries include Roman trading ships and a 17th century Cossack raiding fleet.

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The researchers initially set out in 2015 to search the sea bed in the area to better understand the impact of prehistoric sea level change.

The team searched 800 square miles of sea bed using specialist remote deep-water camera systems capable of supplying high-definition imagery from deep below the surface.