Melbourne Metro Tunnel's Tunnel boring machine (TBM) Joan launched from Parkville station on October has reached the State Library station on 20 December after boring one-kilometre stretch.

The second TBM Meg which is boring a parallel tunnel is expected to make her own breakthrough in the coming days.

Then both TBMs will be transferred through the station box and then relaunched for the final leg of tunnelling, connecting State Library Station with Town Hall Station.

Metro Tunnel's two other TBMs, Alice and Millie, are busy boring parallel tunnels from the Anzac Station to the Town Hall Station.