1406 AD
One of the biggest Treasure Ships of the First expedition of Zheng He gets lost in the "Western ocean". (
http://en.wikipedia.org/wiki/Treasure_ship )
The ship's cargo consists of: wheat, rice, other cultivated plants seeds, as well pigs, sheep, horses, cattle, goats, chicken... and lots of cultivating and other machinery units, BOOKS, gunpouder and firearms ... like a mini-Noah's ark.
The crew of about 1000 men consists of craftsmen, builders, engineers, metalworkers, scientists, teachers and soldiers. No chinese women with them onboard of course.
The ship after several weeks of sailing without navigation wrecks at
http://en.wikipedia.org/wiki/Swan_River_(Western_Australia)
The
http://en.wikipedia.org/wiki/Noongar locals inhabiting the south-west tip of Mediterranean climate ( of about 200 000 km2 area ) amount no more than 12 000 of all the about half million people of the aboriginal total population.
How this noongar-chinese blend will evolve, let alone to ferment for 400 yrs on this vast, fertile ground?
Language & Writting system ( perhaps noongarian imperial "mandarine" or "latin" as spoken language encoded in hierogliphic chinese characters )? Genetics? Religion? ( fusion of Confucianism + Dreamtime, spiced with a little bit islam )? Technology ( it seems that this territory is rich enough in minerals so early 15th century tech to survive and evolve + steady influx of import tech via the
http://en.wikipedia.org/wiki/Brouwer_Route from the 1610s onwards ... )? Territorial expansion? Demographics?
How this country/society/... will look like in early 1800es when discovered?