The man went overboard on the Quantum of the Seas at about 11pm local time (early Wednesday night AEST), about 1400km south of the Hawaiian islands.
Passengers were asked to go back to their rooms and make sure all their travelling party was accounted for, while bright lights swept the water to search for the reported missing passengers.
About 90 minutes later, the passengers were told they could leave their rooms.
The cruise ship, operated by Royal Caribbean Cruises, has been at sea for 15 days and was due to dock in Honolulu, Hawaii, soon, after a recent visit to Tahiti.
It departed Brisbane with plenty of Australians on board.
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Just hours before the man went overboard, there was a Dawn Service to commemorate Anzac Day on the ship.
His identity is not yet known, nor how it is that he went overboard.
A US Coast Guard Hercules helicopter has taken up the search this morning, flying over the area where the man fell into the water.
The Coast Guard has also put out a call to the US Navy for aid.
The Quantum of the Seas has resumed its course for the Hawaiian island of Kona.