Extending a major underground concourse for commuters towards the western end of Sydney's Central Station will form part of a longer term overhaul of Australia's busiest train station.

About 270,000 people enter or exit Central Station every weekday, and many more use it to switch between trains via its rabbit warren of underground links.

Transport authorities believe improving pedestrian flows at the station will become even more critical when Sydney's new light rail line opens in 2019.

The government unveiled plans in March for a so-called Central Walk, which will comprise a 19-metre wide pedestrian concourse beneath platforms 16 to 23 near the station's eastern end, and a new entrance from Chalmers Street.