Rail stations on a new line in Sydney have been finished one year ahead of schedule and $100 million under budget, but that does not mean anyone will get to use them just yet.

New South Wales premier Mike Baird has announced the railway stations on Sydney's new South-West Rail Link are not complete, but it could be over a year before trains start running.

The Premier toured the new Leppington and Edmondson Park stations, praising the early completion alongside Transport Minister Gladys Berejiklian.

But Ms Berejiklian could not give a date for when they will actually be used.

“I am absolutely confident we will have passengers sitting on trains on the south-west train line in 2015,” she said.

“When exactly in 2015 will depend on how we go in the next few months.

“It means people will be able to get off the roads and onto public transport.”

The state government says the area will see tens of thousands of homes built in the next few years, and it expects hundreds of thousands of new resident to use the new rail line.

Work on the South-West Rail Link began in August 2009, and now includes the new twin train line from Glenfield to Leppington via Edmondson Park.

Reports say 95 per cent of train signals are now in place, along with 80 per cent of overhead wiring.

The NSW government says it is looking at rail and communications systems, and will spend some time testing the new infrastructure and training staff as well.

NSW transport planners are reportedly also looking for a new land corridor to connect the South-West Link to the new Sydney airport to be built at Badgery's Creek.