A new train service to Melbourne Airport could be up and running within nine years under plans unveiled by a new consortium offering to build the $15 billion project.

Key points: The proposed $15 billion project will be split three ways: between the Victorian and Federal Governments and the private consortium

The proposed $15 billion project will be split three ways: between the Victorian and Federal Governments and the private consortium There will be 27 kilometres of new track, including two tunnels

There will be 27 kilometres of new track, including two tunnels Sunshine station will be upgraded to a superhub and a new underground station would be built at the airport

The AirRail Melbourne consortium includes superannuation fund IMF Investors, Melbourne Airport and Metro Trains and will contribute $5 billion to the plan.

The Federal and Victorian Governments will contribute $5 billion each, and the project would be built in six or seven years starting in late 2020 and opening a year after Melbourne Metro opens in 2027.

"What this means is together with government, this project will now total $15 billion and mean Victoria finally gets a world-class airport rail service and so much more," project leader Danny Elia said.

Under the plan, 27 kilometres of new track will be built between Southern Cross station in Melbourne's CBD and Melbourne Airport via a new "super hub" in Sunshine.

New airport train station

There will also be twin tunnels between Southern Cross station and Sunshine and a new underground station at the airport.

"To achieve an excellent world-class customer experience, it is integral to have an underground station at the airport and that's what we'll be building as part of this proposal," Mr Elia said.

"It will mean seamless world-class experience using specialised airport trains and a ticket price of under $20, meaning you won't only save time but also money."

The service will deliver a "reliable" 20-minute travel time from the CBD to the airport for $20, with around-the-clock services running every ten minutes, Mr Elia said.

An artist's impression of the inside of a new proposed underground train station at Melbourne Airport. ( Supplied )

Asked if he thought it was the right price, Victorian Premier Daniel Andrews said: "Ultimately you've got to always be conscious of value, otherwise people won't use it."

He expects there to be interest from other private sector partners in the project.

"We'll work through the detailed proposal that they've put forward in the usual way, in a methodical way," he said.

"I did say in relation to the airport rail and suburban rail loop that there would be a stampede from the private sector to be involved in these projects. They're the biggest public transport infrastructure projects in the country's history."

Project for 'all of Victoria'

The twin tunnels at the centre of the project will be the key to unlocking more capacity in the metropolitan rail system in the city's west and linking up with regional areas.

The tunnels will be used by the airport rail link for one third of the time and providing for more trains coming in and out of the city from places like Geelong, Ballarat and Bendigo.

Mr Elia said the plan would unclog congestion and cut 10 minutes from train trips.

The rail link to Melbourne Airport could start as early as 2020. ( ABC News: James Hancock )

There will be more than 10,000 new train trips each peak hour for people in the city's west, Mr Elia said, and it would take thousands of cars off the roads.

He said the private consortium "supercharges" the project to make it more than just a link to the airport.

"It's a complete gamechanger for people in the regions and in the western suburbs of Melbourne trying to get into and out of the city," he said.

"What the route through Sunshine means when you compare it to any of the other options being considered is two million Victorians get to enjoy the benefits of this airport rail link."

Mr Elia said more than seven million Australians would own a piece of the "nation building" project through their superannuation.

The plan comes as the Victorian Government promises $150 million to increase the number of carparks at suburban train stations by 20 per cent.

That equates to 11,000 parking spots on top of the 55,000 already available.

There will be an extra 1,500 new parking spots along the Cranbourne and Pakenham lines, including 400 at Cranbourne station and 450 at Pakenham station.