11:45 AM PT -- A representative for the Royal Bahamas Defense Force confirmed to TMZ ... The 66-year-old woman jumped from the 14th floor of the cruise ship. Search and rescue efforts were officially called off Wednesday.

The Taylor Swift-themed cruise from Florida to the Bahamas went from happy to sad Tuesday ... as a 66-year-old woman fell overboard and is now missing.

A rep for the U.S. Coast Guard tells TMZ ... the Royal Caribbean cruise ship filled with Taylor's "Swifties" left the Port of Miami Monday and was about 17 miles north of Nassau in the Bahamas when tragedy struck Tuesday night.

According to the spokesperson ... the woman tumbled off the ship called Allure of the Seas, plunging into the ocean at about 9:40 PM.

The Royal Bahamas Defense Force, assisted by the U.S. Coast Guard, responded and conducted search and rescue efforts, using helicopters and airplanes.

But, so far, the woman has not been found and is considered missing.

The cruise was supposed to be a fun get-together attended by Taylor's most ardent fans to celebrate the pop star's career.

Ashley Sindaco and Marie Sindaco, who are on the cruise, joined us on "TMZ Live" Wednesday, where they gave a first hand account of what went down Tuesday evening. Watch the vid ... they recall the search efforts that were executed over the course of several hours ... including how a sister cruise ship came over to the scene to help.

But, it's now turned into a nightmare as rescuers comb the waters to find the missing woman. It's unclear if she was part of the Swifties contingent or a separate group. It should be noted that Taylor herself is not involved in the cruise.

As you know ... TMZ broke the story Monday about the Taylor-themed bash, posting a bunch of photos showing the Swifties having a blast onboard the ship.

A Royal Caribbean spokesperson tells TMZ ... "Our crew immediately launched a search and rescue effort and is working with local authorities. We are also providing support and assistance to the guest's family during this difficult time. To respect the privacy of our guest’s family, we have no additional details to share."