Melbourne would get a significant tourism boost if a man-made island able to dock luxury cruise ships was built in Port Phillip Bay, according to Melbourne lord mayor Robert Doyle.

With luxury cruise liners getting bigger and bigger, and Station Pier getting older, building a man-made island in the bay was an idea worth considering, Cr Doyle said.

The world's largest cruise ship, Harmony of the Seas.

From the island, international visitors could then be ferried up the Yarra River to Docklands, putting them within "a one minute walk to a tram, the iconic Melbourne way to come into the city," Cr Doyle said.

"Why not think outside of the square? Why not think about something like - as has long been mooted - an island in the middle of Port Phillip Bay? And to create an artificial island there which could have tourist facilities, where we could provide specialty docking for these super luxury liners, no matter how big, both now and into the future. And then bring them into the heart of the city into Docklands, through ferry activities like Paul Little's. And that would be a much more pleasant sort of arrival into Australia and Melbourne," Cr Doyle said.