A passenger has jumped overboard from a cruise ship sailing to a huge international city popular with millions of tourists, with a frantic search and rescue mission now ended. A man in his 30s plunged into the sea, 30km northeast of Moreton Island, near Brisbane, on Friday night after he "apparently climbed over the safety railing and jumped".

Emergency services quickly arrived at the scene and carried out a search of the water for the man. A Carnival Cruise Line spokesperson said the family of the passenger notified the crew. CCTV footage appeared to show the man climbing over the safety railing before jumping into the water, a spokesman said.

"The male guest was travelling with family who alerted the ship's crew of a possible missing person, and a review of the CCTV footage confirmed the guest's action,' a Carnival Cruise Line spokeswoman said.

"All appropriate authorities have been alerted and Carnival will assist authorities in their investigation upon the ship's return to Sydney.

"Carnival's Care Team is supporting the guest's family and our thoughts and prayers are with them and their loved one."

The ship was sailing from Moreton Island towards Sydney when the incident unfolded overnight.

The Australian Maritime Safety Authority (AMSA) led the operation with support from Queensland Police, deploying five rescue helicopters, six surface vessels, and Challenger jets in the search.

After a day of intensive searches AMSA confirmed the rescue mission had been suspended at 5.30pm on Saturday.

"Following an intensive air and sea search involving multiple assets, the missing person was not located and AMSA has now released all assets from tasking," an AMSA spokesperson said.

It comes after another passenger drowned just hours earlier at Moreton Island on Friday. The woman was snorkelling when she ran into difficulty and, despite being pulled to shore by an off-duty lifesaver, she died at the scene.

A report is now being prepared for the coroner. The two incidents are not thought to be connected.