A team of scuba-diving archaeologists have discovered an undersea settlement that could be 10,000 years old.
The team found evidence of a Stone Age civilisation
The divers were honing their skills in preparation for a more detailed search further away from Tyneside.
But they found what is believed to be the country's second submerged Stone Age development, while practising in the North Sea off Tynemouth.
Another slightly more recent site, still from the Mesolithic era, was also found on the seabed nearby.
The settlements came to light when Dr Penny Spikins of Newcastle University noticed some flints on the seabed, which she instantly recognised as being significant.
Dr Spikins, leader of the international research team behind the Submerged Prehistoric Landscapes Project, said: "I was learning to scuba dive and was in the middle of a training session in the sea when I noticed lots of pieces of flint beneath me on the sea bed.
"To the average person they would seem like ordinary stones you would find on the beach, but to a specialist they were something very exciting indeed."
Among the flints, the team found an arrowhead and cutting implements with a serrated edge.
One settlement is thought to date back to the late Mesolithic period, 8,500 to 5,000 years ago, while the other, found further out to sea, is thought to be early Mesolithic, 8,500 to 10,000 years ago.
Mesolithic people were hunter-gatherers and lived in the Middle Stone Age - between 5,000 and 10,000 years ago.
Both sites would have been gradually submerged as sea levels rose following the end of the last Ice Age.
The precise location of the sites is being withheld for their protection, but the experts said they were off the Tynemouth coast.
The Newcastle team made the discovery off Tynemouth
Dr Spikins added: "We think that Tynemouth could have been an important place for the early settlers, because as well as having the luxury of coastal resources they had the River Tyne nearby."
Archaeologists always suspected that there were sites to be found under the British North Sea after a fishing trawler picked up a Mesolithic antler harpoon there early last century.
But the Newcastle University team has found the first evidence since then.
Dr Spikins said: "Archaeologists thought that the sites left by people who lived 5,000 to 10,000 years ago had simply been lost to the sea.
"But our finds could change our understanding of the earliest occupation of the British Isles."
English Heritage's chief archaeologist David Miles said the discovery gave a
glimpse of the "prehistoric Atlantis" which linked modern Britain to continental Europe.
He said: "This is a tremendously exciting discovery.
"We know that there is a prehistoric Atlantis beneath the North Sea where once an area equal to the size of present day Britain attached us to the continent.
"It is potentially an area for exploration and this discovery by the Newcastle University team gives us a stepping stone into this unknown world."