A British cruise passenger has reportedly fallen overboard in the Adriatic Sea, prompting a desperate search.

Officials in Croatia have said a young Briton on board Royal Caribbean's Explorer of the Seas ship hasn't been seen since the early hours of Friday (August 9).

Passenger, Nicole Bullock, wrote on X: "Woken up on the cruise ship around 3.40am to the emergency message 'Oscar Oscar Oscar off the port side'. Man overboard.

"Been watching the rescue efforts off my balcony all day, hoping for a positive outcome."

It isn't clear if the missing person is a man or a woman, but it is believed the Explorer of the Seas is on a seven day route around Greece and Croatia, with the journey having started on August 3.

A search and rescue operation has been ongoing near the island of Jabuka, according to the Mirror.

Royal Caribbean has been approached for comment.

The Foreign, Commonwealth and Development Office is aware of reports of a person overboard and is in touch with the cruise company.

A spokesperson for the Foreign Office said: "Our staff stand ready to support British nationals overseas 24/7."