Eighteen metres below ground on the site of an old central Auckland food court, workers are burrowing a "construction artery" for the country's deepest rail station.
It's the next step in the ongoing construction of the City Rail Link (CRL), as Link Alliance builds the Karangahape Station as part a contract for the project's main stations.
The station will ultimately join with twin CRL tunnels to the Mt Eden, Aotea and Britomart Stations, before linking up with Auckland's wider rail network.
But businesses and pedestrians along the busy central street won't hear the hammering construction under their feet, thanks to a huge noise enclosure dampening the noise.
Half the size of a rugby field towering above the access shaft, the acoustically insulated noise enclosure will muffle the sound of the 24-hour mining operation, Link Alliance's Dale Burtenshaw says.
"The noise enclosure is a bit like a silencer on a car, reducing the impact of construction at street level in a busy part of the city around Karangahape Road," he said.
"The enclosure muffles construction noise and gives us the flexibility to work longer hours to get the job underground done without disturbing neighbours living and working around us."
Burtenshaw said mining of the tunnels at Karangahape Station recently began with an initial 15-metre-long connection to the caverns for the station's platforms.
"This connection is short, but it will become an important and busy 'construction artery' for us providing access for people, machines and material," he said.
The connection is being mined from the bottom of the temporary access shaft 18 metres deep, built where once stood the Mercury Plaza food court.
An arch-shaped connection, 9.5 metres wide and eight metres high, will first be mined by a large excavator, Burtenshaw said.
Specialised mining equipment known as a road header – a machine with a boom-mounted cutting head that rotates as it grinds through rock – will finish the first stage of the connection before cutting further underground to mine the station platform tunnels.
The mined platform tunnels – that reach up to 35 metres underground - will stretch 217 metres long to accommodate nine-car trains.
"It's a clear sign of work ramping up," Burtenshaw said.
"Our focus is very much on welcoming the tunnel boring machine at Karangahape Station at the end of next year on the first leg of its journey from Mt Eden."
Meanwhile, work continues on other section of the project, including along Mercury Lane, the site of Karangahape's main above-ground station building.
Twenty of the 26 reinforced concrete panels known as diaphragm walls (d-walls) that are part of the building's permanent underground walls have already been completed.
At Beresford Square, where the second station entrance is located, work to relocate power, gas, water, wastewater and telecommunication services is nearing completion, Burtenshaw said.
Work has begun on installing six plunge columns through the centre of the square, which will provide temporary support for the floor slabs during the construction of the various levels of the station.
Up to 40 metres deep, the columns will be removed once the permanent walls and columns are completed.
The CRL is planned to open in 2024 and is expected to double the city's rail capacity.
The project promises to carry 54,000 people an hour during peaks, reduce rail journey times and double the number of Aucklanders living within 30 minutes of central Auckland - New Zealand's biggest employment hub.