A super fund-backed consortium has proposed building a high-speed subway that could bring travellers from Melbourne Airport to the CBD in 20 minutes.
High-speed trains would get travellers from Melbourne's CBD to the airport in just 20 minutes through a seven kilometre subway under a proposal backed by a multi-billion-dollar superannuation fund.
The AirRail Melbourne consortium, made up of IFM Investors, Melbourne Airport, Metro Trains and Southern Cross Station, would match the $5 billion commitments made by both the Victorian and federal governments, taking the project to $15 billion.
IFM also has a stake in Southern Cross Station and and Melbourne Airport and the consortium has been spending months investigating its proposal, executive director and project leader Danny Elia said.
"What we've designed is a high speed corridor between the airport and the city," Mr Elia told AAP.
Construction under this plan would start early, in 2020 rather than the already flagged 2022, which Mr Elia said was because "we've been working at this for over a year, we're well prepared and ahead of the curve."
The consortium spent six months independently investigating routes and landed on a super hub in Sunshine before the state government announced that as its own preferred route, Mr Elia said.
The Sunshine option means tracks are freed up, cutting commuting time from Geelong, Ballarat and Bendigo, and creating better travel from Wyndham Vale too.
"As we expand our runways and terminal facilities we also need world-class linkages between the airport, city and regional Victoria," Melbourne Airport chief executive Lyell Strambi said in a statement.
"Our vision is for a seamless passenger experience at the airport, properly integrated between the train carriage and the terminal."
Trains would run throughout the day and night, ramping up to every 10 minutes during peaks, and a one-way ticket would cost $20.
The rail line would involve 27km of new track with twin rail tunnels between Southern Cross and West Footscray.
Premier Daniel Andrews on Sunday said the project would always receive "significant" interest from the private sector.
"That's one exciting way of doing it, there'll be others I'm sure of it," he told reporters of the proposal.
Last week Mr Andrews announced last week the register of interest for the project was open, marking the start of market engagement.
Opposition Leader Matthew Guy said the fact that Melbourne Airport itself was a part of the consortium gave the proposal added weight and construction should start sooner.
"There's now $5 billion on the table from the federal government, $5 billion on the table from private industry, it beggar's belief why the state government says it will now take another four to five years to start construction, they should get on with it," he told reporters.
A full business case done in partnership between the state and federal government is still underway, but Victoria says its preferred route is through Sunshine.