The machine digging the 10-mile tunnel under the Chiltern Hills broke through on Tuesday.
The machine digging the 10-mile tunnel under the Chiltern Hills, named Florence after nurse Florence Nightingale, broke through near South Heath, Buckinghamshire on Tuesday.
It was launched in May 2021 near Rickmansworth, Hertfordshire.
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Hundreds of HS2 workers gathered to witness the moment, which was marked by cheers and fireworks.
The machine dug one of a pair of tunnels with a depth of up to 80 metres to be used for HS2 trains travelling between London and Birmingham.
A crew of around 17 people worked in shifts to keep it running constantly as it excavated the tunnel, lined it with 56,000 pre-cast concrete segments and grouted them into position, moving at an average speed of 16 metres per day.
A second identical machine will break through in the coming weeks.
Rail minister Huw Merriman said: “This ground-breaking moment for HS2 demonstrates significant progress on the country’s largest infrastructure project, with Florence paving the way for faster, greener journeys between London and Birmingham while supporting hundreds of jobs and apprenticeships along the way.
“Today’s breakthrough of HS2’s longest tunnel highlights the momentum behind the project and the achievement is testament to the hard work and dedication of the 450-strong team helping deliver the line that will transform rail travel for generations to come.”
Florence will be dismantled over the coming weeks, with some large parts to be reused in other tunnel boring machines (TBMs) while many others will be scrapped.
The three million cubic metres of chalk and other material removed during the tunnelling is being used for a grassland restoration project at the site where the machines were launched.
Two more machines will be launched to excavate tunnels between Old Oak Common and Euston in the capital.
HS2 Ltd executive chairman Sir Jon Thompson said: “Today is an incredible day for HS2 and I’d like to thank the hundreds of people who’ve worked so hard over many years to make it happen.
“Once complete, HS2 will dramatically improve journeys between our two largest cities and also free up space on the existing mainline for more local trains.
“We’ve still got a lot of work to do, but historic moments like today really underline the huge amount of progress that’s been made and the fantastic engineering skills we have on the project.”
HS2 Ltd project client David Emms, who is responsible for the section of the route that includes the tunnel, paid tribute to the workers’ “immense feats of engineering”.
He continued: “HS2 remains the biggest infrastructure project in the UK.
“From tunnels to train stations to structures and systems, the scale and ambition of what we are delivering is unmatched.
“What we are achieving today has helped to set new standards for the construction industry in the UK and around the world.
“Not only that, rail travel for the future is being set by us as well.”
