A spokesman for Rail Projects Victoria said the machines would be launched within the second half of this year. Another two machines were due to start tunnelling from the future Anzac Station below St Kilda Road towards South Yarra by the middle of this year, but the station box where the machines are to be assembled is still being excavated and there are no boring machines in sight. The two extra machines, weighing 1100 tonnes each, are not due to arrive until later this year. They were supposed to arrive by March. Once they are in the ground, the German boring machines - manufactured in China by Herrenknecht - will operate 24/7 and tunnel about 10 metres per day.

Despite the delays, the Andrews government has insisted that this will not push out the timeline of the project. "We have assembled an accomplished team to ensure the Metro Tunnel Project is delivered on time. I have every confidence that these experts will ensure our overall schedule is maintained," Ms Allan said. It is unclear if this has contributed to the project's $2 billion blowout so far - a cost to be worn by the consortium Cross Yarra Partnership (CYP), led by Lendlease, John Holland Group and Bouygues Construction Australia.

Loading Replay Replay video Play video Play video Key to achieving the project's deadlines will be finishing the complex State Library and Town Hall caverns by the time the boring machines are set to reach them. Sources close to the project are concerned that the caverns being dug beneath the CBD are falling behind schedule, but the government has refused to say when each station or stage of tunnelling will be complete. "The project is proceeding as planned and key milestones are being achieved, however, it isn’t always possible to give specific dates for completion of various stages," Ms Allan said. The Victorian Auditor-General warned last month that the State Library Station faced delays due to difficult geological conditions, slow rates of construction and lagged planning approvals.

Last week, the government celebrated the excavation of a 200-metre long tunnel beneath Swanston Street, which forms the first stages of the State Library cavern. The first of the tunnel boring machines is being put together, on site, in North Melbourne. An extra two tunnels – one on either side – still need to be dug to complete the shape of the cavern. It is through these twin tunnels that the tunnel boring machines will enter the cavern, of which 20 per cent has been excavated. The second cavern, to be built at Town Hall Station, is less progressed than State Library. Road header machines needed to carve out the cavern for the Town Hall station have not yet been lowered at the site, due to a lag in building a large acoustic shed designed to block out noise and dust.

The shed was supposed to be finished late last year but it is not yet half built, and is expected to be finished later this year or early next year. Construction of the Metro Tunnel's Town Hall station at City Square. The acoustic shed is partly built. Credit:Joe Armao The Andrews government has previously said that tunnelling, which is expected to take two years to complete, would be finished by 2021. But a Rail Projects Victora spokesman said schedule changes were "not unusual with projects of this complexity". Opposition Transport Infrastructure spokesman David Davis said delays on the proejct risked driving up costs.