TBMs will be used to excavate the twin-bore tunnel between the new CBD South and Domain stations on an alignment east of the Princes Bridge 11m beneath the surface and 7m below the river bed.

Andrews also announced that the state government has now secured around $A 4.5bn ($US 3.3bn) in funding, around half of the total budget for the project.

The 9km Metro Rail tunnel will include five new stations and is intended to relieve the existing City Loop line, creating additional capacity through the city centre.