Stena Line services between Belfast and Cairnrayan were disrupted earlier, following a fire on board a ship docked at Belfast port.
Thirteen fire engines and 61 firefighters responded to reports of the blaze shortly after 5am on Sunday.
Stena Line said it was a small fire in the exhaust system of the Superfast VII vessel and was brought under control by crew.
They said no passengers had been on board and all crew members are safe.
A spokesperson said: "As a result of the incident, the 0730hrs sailing from Belfast and the 1130 hrs from Cairnryan have been cancelled.
"The next departure from Belfast will be the 1130 hrs (Stena Superfast VIII) and the 1530hrs (Stena Superfast VII)."
The Fire Service said investigations are ongoing.