Expressions of Interest (EOI) are now being sought to deliver the new Melbourne Metro Rail tunnel, Australia's biggest transport project, through a Public Private Partnership – expected to worth up to A$6 billion.

The massive project will deliver the nine kilometre twin tunnels under the city centre and five new underground stations at Arden, Parkville and Domain and two new city stations connected to Flinders Street and Melbourne Central.

Fully funded by the State Government of Victoria, the project has attracted significant interest from some of the world's biggest construction and engineering firms.

The new Metro Tunnel will give the Cranbourne, Pakenham and Sunbury lines their own tunnel through the city centre, which will free up space in the Loop to run more trains in and out of the city.

Sixty-five brand new, high capacity trains will run on the line, freeing up more trains and more space all over Melbourne.

When the project is completed, more trains will come more often, to more stations, meaning less traffic congestion in the suburbs.

Early works begin next year, with the major construction delivered through this package to start in 2018, and the project set to create 3,700 Victorian jobs.

The EOI process closes at 2:00 pm on Thursday 9 June. For more information, visit melbournemetro.vic.gov.au or the State Government of Victoria's Tenders website.