Marine archaeologists have found a 2,400-year-old Greek vessel that they believe is the world's oldest intact shipwreck, in the Black Sea off Bulgaria, a British-led team said on Tuesday.

The British-Bulgarian Black Sea Maritime Archaeology Project found more than 60 shipwrecks after surveying some 2,000 square kilometres of seabed.

Carbon dating confirmed that a Greek trading vessel located last year is the oldest known intact shipwreck, said team leader John Adams of the University of Southampton.

"A ship, surviving intact, from the Classical world, lying in over 2 kilometres of water, is something I would never have believed possible," Adams said.

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

The design used to build the ship had previously been seen only in pictures decorating ancient Greek pottery, such as the Siren Vase held by the British Museum, the team said.

The deep anoxic - oxygen free - water at the site of the shipwreck can preserve organic material for thousands of years, they said.

The team includes British, Bulgarian, Swedish, US and Greek marine archaeologists and maritime scientists who used geophysics, sediment core sampling, and underwater exploration to examine changes in sea level following the last ice age.

In addition to dozens of shipwrecks, they found the remains of an early Bronze Age settlement under water near the former shore of the Black Sea.