Rescuers have called off a search which was launched amid fears that a ferry passenger had fallen into the sea.
The man is understood to have boarded the boat at Larne in Northern Ireland but was reported missing after it docked at Cairnryan in Scotland.
Clyde Coastguard was notified shortly after 10am and a full search of the ferry and surrounding area was organised, taking into account tidal drift and winds.
The Portpatrick, Stranraer and Larne RNLI lifeboats were all asked to launch and a Royal Navy rescue helicopter was scrambled from Prestwick.
The search was called off at 1.40pm.
Coastguards said it did not appear that the man had gone overboard, though rescuers have not been able to confirm one way or another.
The Maritime and Coastguard Agency (MCA) said the European Highlander ferry left Larne at 7.24am and arrived at Cairnryan two hours later.
The man was reported missing by a coach driver after the vessel arrived in Scotland.
A Clyde Coastguard spokeswoman said: "We had to do the search because of the possibility that someone went overboard from the ferry but it now does not look as if that is the case."
The MCA said police in Northern Ireland had also been informed.
Ferry operator P&O said: "We can confirm that a passenger who was part of a coach party that boarded the 0730 sailing from Larne to Cairnryan, on the European Highlander ferry, was reported missing on arrival in Cairnryan.
"P&O Ferries has conducted a search of the ship and is assisting authorities with their investigations as to the whereabouts of the passenger, including whether the person may have left the ship in a different vehicle."
The company said it had also alerted the MCA, as is standard procedure.