After 25,000 man hours underground smashing through 206,000 tonnes of crushed rock in north-west Sydney, Elizabeth, the state's premier tunnel boring machine, has punched through the walls of Norwest station in Baulkham Hills.

The event is a milestone in the development of Sydney's north-west rail link – up to 35,000 commuters are expected to flood through Norwest station every day when it opens in 2019.

The public-private project is currently Australia's largest public transport development, with a budget estimated at over $8.3 billion.

On Wednesday, NSW Premier Mike Baird and Transport Minister Gladys Berejiklian announced that the construction of the rail corridor is ahead of schedule and $300 million under budget.