The wreckage of British explorer James Cook's ship HMS Endeavour which has laid in US waters for almost 250 years has been found after a two decade search by maritime archaeologists.

Cook famously sailed the ship around the South Pacific before he landed on the east coast of Australia in 1770.

Australian National Maritime Museum chief executive Kevin Sumption confirmed on Thursday the shipwreck of Cook's vessel had been identified in Newport Harbor, Rhode Island, where maritime archaeologists had been investigating several 18th century shipwrecks since 1999.

However, an American expert involved in the discovery has hit out at the claims, saying it is 'premature' to definitively state the ship is the Endeavour.

The Endeavour was scuttled in Newport Harbour by British forces during the American War of Independence in 1788, where it lay forgotten for more than two centuries.

'It's arguably one of the most important vessels in Australia's maritime history,' Mr Sumption told reporters.

'I am satisfied that this is the final resting place of one of the most important and contentious vessels in Australia's maritime history,'

The last pieces of the puzzle had to be confirmed before I felt able to make this call.

'Based on archival and archaeological evidence, I'm convinced it's the Endeavour.'

'It's an important historical moment, as this vessel's role in exploration, astronomy and science applies not just to Australia, but also Aotearoa New Zealand, the United Kingdom and the United States.'

However, Australia has since been accused of jumping the gun by the lead investigator on the project.

Dr Kathy Abbass from the Rhode Island Marine Archaeology Project claimed the report is 'premature' and that the Maritime Museum is 'in breach of the contract' after the results were shared with the public.

'What we see on the shipwreck site under study is consistent with what might be expected of the Endeavour, but there has been no indisputable data found to prove the site is that iconic vessel, and there are many unanswered questions that could overturn such an identification,' she told the ABC.

A 'legitimate report' will be shared by the RIMAP on its website once the studies are complete.

'RIMAP recognises the connections between Australian citizens of British descent and the Endeavour but RIMAP's conclusions will be driven by a proper scientific process and not Australian emotions or politics,' Dr Abbass added

Several details on the wreck convinced archaeologists they had found Endeavour after matching structural details and the shape of the remains to those on 18th century plans of Endeavour.

Just 15 per cent of the vessel remains with researchers now focused on what can be done to protect and preserve it.

'We will continue to investigate and look closely with maritime experts at Rhode Island about the future of this site and what should happen to this site but certainly protection is what we're working towards right now,' Mr Sumption said.

Originally launched in 1764 as the Earl of Pembroke, the ship was renamed Endeavour in 1768 by Britain's Royal Navy and prepared for a major scientific voyage to the Pacific.

From 1768 to 1771 Endeavour sailed the South Pacific, primarily to record the transit of Venus in Tahiti in 1769.

Cook then sailed it around the South Pacific searching for 'the Great Southern Land', charting the coast of New Zealand and Australia's eastern coastline before claiming the land for Great Britain on August 22, 1770.

Endeavour was later sold to private owners, renamed as Lord Sandwich and was deliberately sunk in 1778 by British forces during the American War of Independence.

A year later Cook was killed in Hawaii during his third Pacific voyage, 10 years before the First Fleet arrived in NSW to establish a British colony.

Researchers are finalising their report on the site, which will be peer-reviewed and published.