The tunnelling process for The Lower Thames Crossing is due to begin in 2028.
National Highways said negotiations to buy one of the world’s largest tunnelling machines were now under way.
It would be capable of digging 60 metres below the Thames, creating a new road link between Essex and Kent, and now enables the project to secure private sector investment to deliver the remainder of the construction.
Next summer, work on the northern tunnel entrance where the tunnel machine will begin its journey will get under way.
Matt Palmer, the Highways Agency’s executive director of the Lower Thames Crossing project, said the crossing was now on track to be built “in the early 2030s”.
The 16.4-metre-wide tunnel boring machine will excavate one of the widest tunnels in the world and it will create the longest road tunnel in the UK.
Tenders are now being welcomed from prospective suppliers who could build the tunnel boring machine.