10,000 people have scrambled to get a spot in the City Rail Link open day on November 17.
The underground walking tour tickets were snapped up within an hour of going online at 12pm today as the public are keen to grab a first glimpse at the construction.
Ewart Barnsley of City Rail Link says the interest in the underground tunnel walk has "exceeded our expectations".
"There has been unprecedented response with 10,000 bookings made within the hour."
The City Link Rail is unable to host more than 10,000 people for the open day. The Waterview Tunnel open day in 2017 hosted 42,000 people but Barnsley has said there are "a lot more health and safety concerns to consider" with the City Rail Link project.
There are no plans from City Rail Link to extend the open day to more people.
"If we had an opportunity to welcome more people on site, we certainly would have done so," says City Rail Link Chief Executive Dr Sean Sweeney.
Organisers have warned the walk is not suitable for those with a fear of being in confined spaces.
"Be prepared for dust, loud noises, and uneven surfaces. Asthmatics should bring inhalers. People are encouraged to wear sensible, flat shoes."
Free supervised bike valet parking will be provided nearby on the day, "as well as bicycles, this facility can secure pushchairs, scooters and skateboards for you".
The City Rail Link, when completed, will connect from Britomart to Mt Eden station, stopping off at Aotea Square and Karangahape Rd.
The project has taken a huge toll on local businesses because of road closures, many will be glad to see the end of construction. The project is not due to be finished until 2024.