A 72-year-old man is believed to have gone overboard during a five-day Princess Cruise trip to Mexico, company officials said.

       The Ruby Princess ship arrived in San Francisco on Monday at 6:50 a.m. at the culmination of a round-trip voyage to Ensenada that departed on Nov 27.

       When the ship returned to California, he was no longer aboard.

       The passenger's disappearance was ruled as a man overboard situation after company officials said they extensively reviewed CCTV footage and the ship was searched several times without success.

       The man was traveling alone, Princess Cruises said in a statement to ABC News.

       His identity has not yet been released.

       U.S. Customs and Border Protection has taken over the investigation.

       "We extend our heartfelt condolences to the family and friends of the guest who was traveling alone," Princess Cruises said.

       The remaining passengers on the Ruby Princess ship disembarked Monday. The ship was scheduled to depart that evening on a 16-day voyage to the Hawaiian Islands.

       ABC News' Jenna Harrison and Irving Last contributed to this report.