On Friday,the first boring machine to snake its way from Waterloo,in the city's south,reached what will become one of two 160-metre platforms for the Pitt Street station,which is part of the second stage of Sydney's $20 billion metro rail line.
Named Nancy,it is one of five giant boring machines churning away to form twin 15.5-kilometre rail tunnels stretching from Chatswood in the north,under Sydney Harbour to Pitt Street station and three others in the CBD,and onto Sydenham in the south.
It is a world away from construction of the last train line to be built under central Sydney. Opened 40 years ago,the Eastern Suburbs railway line was dug using explosives.
At Pitt Street,contractors have excavated about 92,000 tonnes of sandstone to form the station's underground cavern stretching beneath Park Street,in the north,to near Bathurst Street.
Transport for NSW secretary Rodd Staples said construction of the metro line under the CBD was an"incredibly complex engineering task".
"To think that we have got hundreds of thousands of people walking around above us today,really not understanding what is happening below them,"he said in one of the tunnels on Friday.