Ever wonder whether people from Europe visited Australia before Captain Cook did?

Strange finds have the potential to re-write Australia's history, including an old cannon from Darwin Harbour, 1000 year old coins from Tanzania, and small cannons found at Dundee Beach and at Carronade Island off the coast of Western Australia. (ABC (map from Google, small photos supplied):Xavier La Canna)

A Darwin group trying to prove early European visits to Australia's Top End prior to British settlement expects historic artefacts that could re-write the nation's history will be released within weeks.

Heritage expert Mike Owen from the Past Masters group, which includes archaeologists, anthropologists and others, says he is waiting on the University of Melbourne to complete tests that will indicate how old a type of cannon found near Darwin two years ago is.

"I think it will be within weeks, not months," he said.

Two techniques for dating the item are being used, including carbon dating on seaweed remains inside the barrel and another that can determine when sand trapped in it last saw sunlight.

Mr Owen thinks the cannon will date to hundreds of years before European settlement of southeastern Australia in the late eighteenth century.

The cannon, known as a swivel-gun, resembles a type of weapon commonly used by Portuguese sailors in the 1500s, and was located on Dundee Beach southwest of Darwin in 2010 by schoolboy Christopher Doukas.

Extensive analysis from the Museum and Art Gallery of the Northern Territory found it was likely not of Portuguese origin, and its metal composition and style indicated it was possibly made in Asia and brought to Australia by Macassan traders much later than the 1500s.

Curator at the museum Paul Clark said more proof was needed before you could say Portuguese reached Australia.

"It is all very well to have a hypothesis but you need to prove it or you need to show examples and I don't think yet that there has been any evidence, tangible archaeological evidence, that can really point to the fact that they were here," he said.

Mr Clark predicted the Dundee swivel gun would date to somewhere around the year 1780 or 1880.

As well as the swivel gun another old cannon found in Darwin Harbour in 1908 may also be sent off for tests.

That item, which is only 48cms long, was found with another similar swivel gun, which has since been lost.

The surviving cannon has been housed for decades in South Australia.

It is now at the SA Maritime Museum and curator Lindl Lawton said nothing quite like it was known from anywhere else in the world.

Attempts midway through last century to find out where and when the cannon was made, saw it identified by a British expert as a Dutch weapon from the 1600s, but others think it may have been an Asian imitation, due to its lack of decoration.

Ms Lawton said the museum was currently working out the logistics of getting the cannon to Melbourne, but there was no firm plans for this to happen.

Mr Owen said that item also had the potential to show early visits to Australia from Europeans and it may be possible to have the sand left inside its barrel dated.

Not all finds have been in the Northern Territory.

At Carronade Island, off the coast of Western Australia, two small cannons were found in 1916 but analysis found they were also likely to be Asian copies of Dutch guns.

As well as the cannons that Mr Owen believes could re-write Australia's history books, he said there are other artefacts probably out there that had not been properly examined.

One such item was a second swivel gun thought to have been found at Dundee Beach a few years ago that was believed to have been seen by a Telstra worker the day before Clean Up Australia Day.

The worker picked up the item and looked at it, but when he later went back to the beach to retrieve the item but it was gone, and was believed to have been taken to a tip, Mr Owen said.

Efforts to contact the man who found the item by the ABC were unsuccessful.

Previously coins from the Tanzanian port city of Kilwa were located on a remote island off the coast of Arnhem Land, leading people to speculate that travellers from Africa made it all the way to Australia 1000 years ago.

Analysis of those coins continues.

Ian McIntosh is an anthropologist from Indiana University in America and he also believes there are gaps in Australia's history.

"The starting point is with the understanding that spices from just north of Darwin found their way to ancient Egypt and Syria 3,500 years ago," he told the ABC via email.

"They were transported by ship and land. Australia was not as isolated as we like to think!" he said.

He said Aboriginal mythology speaks of many groups that predated the Dutch reaching Australia.