The laying of the first stretch of track on the"Skytrain",a 4.5-kilometre viaduct and cable-stayed bridge between Rouse Hill and Kellyville in the city's north west,is also under way.
Assembled in Sri City near Chennai in south-east India,the six carriages of the first driverless metro train to be shipped to Sydney will undergo a final fitout at a new maintenance depot at Rouse Hill.
The fleet built by French manufacturer Alstom for the north west line will eventually boast 22 six-car trains.
Passengers will be able to peer onto the rail track through a window at the front of the single-deck train. Each carriage features three double doors,which will allow the train to be boarded faster.
Transport Minister Andrew Constance said people living in Sydney's north west would get a train every four minutes in the peak in each direction once the line opens in 2019.
"After that,services will extend into the CBD by 2024 – which will have an ultimate capacity of a metro train every two minutes in each direction under the city,"he said.
The 36-km Sydney Metro Northwest from Rouse Hill to Chatswood is the first stage of a line that will extend onto the CBD,Sydenham and Bankstown. The government has put the cost of the second stage at between $11.5 billion and $12.5 billion.
The first stage of the project involves the construction of eight new stations,the upgrade of five existing ones,and conversion of the heavy rail line between Epping and Chatswood to metro standards. The latter will require the from late next year.
The state government has also committed to building a metro line from the CBD to Parramatta via the Bays Precinct at Rozelle in the inner west and Olympic Park.
Under,that new line will be built next decade and be operational in the second half of the 2020s. However,the project is still unfunded.