Immigration NZ national border manager Stephanie Greathead said the man, a passenger aboard the Radiance of the Seas cruise ship, was in custody and was set to depart on a flight back home to Australia tonight.
"Immigration NZ can confirm that an Australian male was turned around at [Port Otago] today."
Neither Ms Greathead, police nor Royal Caribbean cruise line would be drawn on why the man was refused entry to New Zealand.
In a statement, Royal Caribbean said it was "cooperating fully with New Zealand Police and Customs in this matter."
The 293m cruise ship, with a capacity of 2501 passengers and 859 crew, departed Sydney on Wednesday, arriving today in Dunedin en route to Auckland on a 10-night cruise.
There were also reports of a sudden death on a cruise ship in Dunedin today but it remained unclear whether it was on Radiance of the Seas or Golden Princess, also berthed in Dunedin.
A police spokeswoman said the death was not suspicious and had been referred to the coroner.
