The excavators will bore a 10 mile (16km) tunnel through part of the Chilterns, from a site near the M25 to near South Heath in Buckinghamshire,
They have been named Cecilia and Florence, after Buckinghamshire-born astronomer Cecilia Payne-Gaposchkin and Florence Nightingale, following a public vote from a shortlist of suggestions made by local schoolchildren.
The plans for HS2 were first outlined more than a decade ago. The initial stage, due to be completed between 2028-31, will connect London and the West Midlands, while the second section will extend into the East Midlands and north of England.
HS2 minister Andrew Stephenson said: “HS2 will provide better, more reliable connections that truly level up our country, boosting economic growth and sharing opportunities.”
They will run almost non-stop and are expected to take about three years to excavate the tunnel, which will be lined with concrete.