The man went overboard the Sun Princess about 10.40pm NZT yesterday at a point about 320km east of Sydney.
The ship turned back this morning but there was no sign of the man.
A Princess Cruises spokeswoman said the man was an Australian resident.
At the time of the incident the Sun Princess was returning to Sydney on a 13-night New Zealand cruise, she said.
"Sun Princess is expected to arrive in Sydney early tomorrow morning."
Passengers onboard had received regular updates regarding their delayed arrival in Sydney and were being assisted to make onward travel arrangements.
AMSA sent a Dornier search and rescue aircraft to the search area.
"There have been no sightings of the man during the search," AMSA said this afternoon.
"Expert medical advice received by AMSA indicated the man was very unlikely to have survived when he entered the water given the height. The advice also indicated that the man would not have been able to survive in the water...given his age, clothing and weather conditions at the time of the incident," AMSA said.
"Sea conditions in the area were rough with swells up to three metres.
"In consultation with the Master of the Sun Princess, the operating company and the next of kin, the search effort has concluded."
DO YOU KNOW MORE? EMAIL US HERE
A cruise ship safety campaigner said the industry had ignored pleas to increase the height of railings on ships.
Kendall Carver, International Cruise Victims (ICV) chairman, said "man overboard" systems would save lives. "When somebody does go overboard a cruise ship, it could be hours or days" before anyone knew, Mr Carver said.
Mr Carver said "man overboard" systems could include lasers that automatically detected any falling human body and immediately alerted crew.
Cunard ship Queen Victoria was reportedly testing a man overboard system earlier this year.
239 people were lost overboard cruise ships internationally since 2000, according to the cruisejunkie.com website. The website said 16 of these cases were from Princess ships.
This year, 19 people were lost overboard, 2 of them from Princess ships, the website stated.
The US Cruise Vessel Security and Safety Law was passed in response to campaigning from ICV.
It said ship rails should be 42 inches (106.7cm) above the cabin deck. ICV wanted a minimum height of 137.2cm.
The law said ships should also integrate technology used for capturing images of passengers or detecting passengers who have fallen overboard, to the extent such technology was available.
Passengers were due to board Sun Princess today for a 14-night cruise to Fiji and other South Pacific destinations, the cruise company said. They had been advised of the 24 hour delay in the start of their cruise and encouraged via direct messages not to come to the cruise terminal today.
