The tallest building in the Southern Hemisphere is being planned for Melbourne's CBD.

Designs for the 108-storey project, aptly named 'Australia 108', are being finalised and, if approved, the skyscraper will be the 18th-tallest in the world.

The 388m structure will feature 600 apartments, a two-storey lobby on the 83rd and 84th floor boasting bars and restaurants, and a 228-room hotel with a sky-deck on top have been added to the initial proposal.

The tower, planned on a site next to the Eureka in Southbank, will stand 65 metres above the Gold Coast's Q1 Tower and 91 metres above its neighbour.

The men with the big vision, architects Fender Katsalidis, who also built the Eureka, said it is the right building in the right place and will become an iconic centrepiece for Melbourne.

"The idea of a significant building is a very good thing for Melbourne," Karl Fender told Seven News.

"We're interested in building on Melbourne as the most liveable city."

Nonda Katsalidis added: "The hotel will mean that people can actually go up and enjoy the building. It becomes open to the public.

"It makes it an accessible building rather than an enclosed residential enclave."

Architects were granted planning permission for a 288m apartment building on the Southbank site in 2010, despite objections from the Melbourne City Council.

The revised super-sized design for 'Australia 108' will be subject to a new planning application.

Australia 108: Two-storey sky lobby. Picture: Fender Katsalidis Architects

The Victorian Government says it is firmly on side.

Planning Minister Matthew Guy told Seven News: "It builds on what we've been calling for, which is a large, dense, 24-hour CBD, an area which can take the pressure off our existing suburbs.

"We're certainly excited by the concept, but we will await a decision on the proposal."

Australia 108: Level 83 skyroom. Photo: Fender Katsalidis Architect

But critics have their doubts.

Melbourne Mayor Robert Doyle said: "We've got to keep an eye on where we want areas like the Southbank going. We don't want a canyon of enormous buildings with no life at street level."