Minister for transport and infrastructure Mr Andrew Constance made the announcement at an industry briefing in Chatswood, which was attended by more than 450 people.

"We've now taken the next step and opened expressions of interest for tunnelling, asking industry to partner with us in delivering this city-shaping project," Constance says.

The first TBM will be launched on the Chatswood - Sydenham section by the end of 2018 and the Sydney Metro City & Southwest project is due to be completed by 2024.

Tunnelling on Sydney Metro Northwest was completed in January this year, with services expected to start in the first half of 2019.

Sydney Metro City & Southwest will extend the Northwest line through the centre of Sydney, using parts of the existing heavy rail route to Bankstown.