An Australian explorer has begun a search for a Portuguese shipwreck off Australia’s northeast coast that, if found, could rewrite how the continent was discovered.

“I’ve got some very strong clues of a possible Portuguese discovery of Australia,” 78-year-old filmmaker Ben Cropp said.

The discovery would be significant because the first records of non-indigenous mariners to visit the continent credit Dutch explorers for sailing here as early as 1606 to chart the west coast of the continent’s northern Cape York Peninsula. Famed English Captain James Cook charted the continent’s east coast in 1770, which later opened the door to British colonization.

Cropp, a self-described "wreck hunter," set off Sept. 20 on his two-month expedition to the coast of Cape York from his base in Cairns -- the gateway to the Great Barrier Reef. Cropp says two Portuguese ships and a Spanish vessel were lost near Cape York in the 16th century, prior to the arrival of the Dutch.

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“It’s important,” he said. “It’s all about Australia.”

Cropp’s team has produced more than 150 documentaries and films for several international media organizations, like National Geographic.

Among Cropp’s previous discoveries was the remains of the HMS Pandora, which is regarded as one of the most significant shipwrecks in the Southern Hemisphere. The British frigate ran aground in the Great Barrier Reef at the edge of the Coral Sea and sank in 1791, killing many onboard. Cropp and two others discovered the wreck in November 1977.

Cropp has searched for evidence of pre-Cook Portuguese exploration of Australia’s east coast before, without success.

“I’m sure the Portuguese were here first, but proving it is very, very difficult,” Cropp said.

But now Cropp says he has new evidence that may indicate the Portuguese made landfall along Australia’s northeast coast as early as 1522. Among the clues: a ship’s cannon, ballast and 16th century European maps that seem to show a detailed outline of Australia.

One European map produced in 1542 shows a large sixth continent located in the position of present-day Australia, called "Java-la-Grande" in many similar charts and navigational aids.

“There’s a whole lot of little finds, but none of them give you a true date -- and that’s what I’m searching for,” Cropp said.

The South Pacific coast of the present-day state of Queensland was notorious for shipwrecks.

Historians estimate there are about 1,400 shipwrecks here.

Strict preservation laws protect the sites. They provide crucial evidence in unlocking and understanding the country’s past.

“It is something that we take very seriously,” said Queensland Environment Minister Andrew Powell. “Depending upon the circumstances of when they were lost, ships can almost in some ways become a time capsule -- a moment frozen in time -- with some of that historical and archeological information that we as a society need.”

Researchers and historians believe European and even Asian vessels were sailing in Australian waters for years prior to Cook’s arrival, but finding hard evidence has been difficult.

“There is a possibility that a non-indigenous vessel visited northern and east Australia before Cook,” Powell said. “But attempts to date to locate evidence of a pre-Cook vessel have been proven to be unsubstantiated.”

Some historians also believe the Portuguese government’s policy of secrecy at the time may have contributed to the suppression of its possible discovery. Additionally, the Great Lisbon Earthquake in 1755 may have destroyed vital records of the country’s exploration of coastal Australia.

Cropp says another reason why finding a vessel has proven impossible is the growth of thick coral at the site of shipwrecks. Cropp estimates any wreck of a 16th century Portuguese ship would now be buried under 6 feet (2 meters) of coral.

The current conditions of finding an early Portuguese shipwreck require that Cropp first snorkel above areas of the seafloor he believes could contain more evidence. Then, he must take a closer look by SCUBA diving.

“You can’t find it by other technology,” he said. “It’s mostly visual.”

It’s meticulous, time-consuming work.

“I know these items are there,” Cropp said. “And I’ve just got to find them.”

What he doesn’t expect to find is treasure, which he says the ships wouldn’t have carried since their main purpose was exploration.

But the real treasure of the discovery may be Cropp’s imprint on history.