The Harmony of the Seas (Oasis 3) class ship leaves the STX Les Chantiers de l'Atlantique shipyard site in Saint-Nazaire, France, March 10, 2016. [Photo/Agencies]

STX has built 120 cruise ships over its 150 years, and has another 11 lined up for the next decade.

Several hundred workers were still busy putting finishing touches to Harmony of the Seas before it leaves the port on Sunday, weather permitting, sailing for Southampton in southern England.

From there, it will embark on for its official maiden voyage on May 22 to its new home port of Barcelona, after which it will begin regular cruises through to late October.

The cruise company has already ordered a sister ship.