US company Utopia Residences has revived its plan to build a $1.1bn luxury cruiseship featuring permanent apartments for the super-rich.

Launch is planned for 2021 and the 190 flats have already been selling for between $4.4m and $36m, its boss has said.

David Robb, founder and chairman of the Utopia project, told Business Insider: "We describe it as the largest private yacht in the world.