New South Wales premier Mike Baird and minister for transport and infrastructure Andrew Constance marked the breakthrough by revealing the design for Showground – one of eight new railway stations being delivered on the AU$8.3bn (£4.2bn) project.
Showground station is being built underground with platforms about 20 metres beneath the surface, providing access to existing residential development, the Castle Hill Showground and nearby employment areas.
"This is Australia’s largest public transport project – the rapid progress being made shows when we start a major project we power on with delivering it as quickly as possible,” said Baird.
Constance added: "The North West Rail Link is the first stage of Sydney’s new rapid transit railway system and will provide a significant boost to capacity across the network.”
The North West Rail Link is ahead of schedule with services to start in the first half of 2019, delivering a train every four minutes in the peak.
The first tunnel boring machine, Elizabeth, started tunnelling in September last year – four months ahead of schedule – and is now halfway through her 9km journey from Bella Vista to Cherrybrook.
Over the coming weeks, TBM Elizabeth will undergo maintenance as she is moved through the Showground station area, before setting off again towards Castle Hill station and then on to Cherrybrook where she will be pulled from the ground.
The four TBMs in the ground have so far built more than 12km of new tunnels, well over a third of the new 30km tunnelling task. The twin 15km tunnels from Bella Vista to Epping are Australia’s longest-ever railway tunnels.