When Paul Rossington, 30, and Kristen Schroder, 27, failed to turn up when the ship docked at the cruise terminal in Sydney Thursday, cruise staff contacted police.
When a search of the ship failed to locate the pair, officers reviewed CCTV footage, which showed them going overboard from the mid-deck at 8:50 p.m. local time Wednesday.
The disappearance is not being treated as suspicious, but it isn't clear if the couple jumped or fell, said New South Wales Police Marine Area Commander Mark Hutchings.
We believe they were up mid-deck, which is half way up the side of the ship which is quite away to fall," he said. "At the moment I've said to my staff it's game on and we are going to be pulling out all stops to try to find these people."
Search and rescue aircraft and marine vessels have focused their search on an area 60 nautical miles east of Forster, between Sydney and Gold Coast.
The incident, aboard the Carnival Spirit, is just the latest in a cascade of woes for the beleaguered Carnival Cruise Lines this year.
Celebrity Families of 2014 [PHOTOS]