There will be no trains for the first visitors to the nation's newest international airport to connect to when they arrive at all hours of the day and night but the area will eventually receive additional rail routes.

The federal government has earmarked about $1 billion to help secure land for rail corridors between Sydney's southwest and the soon-to-be-opened Western Sydney International Airport.

It comes amid potential further delays to an under-construction driverless railway connecting the airport to western Sydney.

The funds announced on Thursday - and quickly matched by the coalition - are hoped to one day extend rail south of the airport and boost connections for one of the fastest-growing parts of Australia.

The announcement paves the way for metro or JetBlack train extensions from the new suburb of Bradfield - just south of the airport - to Leppington and Macarthur, providing access around the area and to the Sydney city-centre.

Currently, Leppington residents who want to reach Bradfield - some 13km away - have limited options: they can drive for 15 minutes or spend more than two hours navigating the bus network.

"We don't want residents of Sydney's southwest to have to rely on buses to get to the airport," Prime Minister Anthony Albanese said.

"We want them to have fast, frequent rail access, and our investment today will help deliver that."

Shadow treasurer Angus Taylor said more investment in rail connections was needed and the coalition would match the announced funding.

"It needs to continue on. The rail needs to go south of the airport and we will absolutely back that," he told reporters in Sydney.

It is unclear when the new rail corridors will be delivered as the timelines have yet to be finalised with the state government.

The federal government funds follow its $195 million contribution to a joint business case with its NSW counterpart to explore future rail connections in Sydney's west.

Construction is already under way for a new metro line between St Marys and Bradfield, due for completion by April 2027, but the 24-hour airport is slated to open in 2026.

Sydney Metro chief executive Peter Regan recently told a NSW budget estimates hearing the timeline for delivery was tight to begin with but the project had faced additional challenges including global supply chain issues, and could be further delayed.

"We're working through with the consortium whether that date for final completion remains the appropriate date," he said.

Liverpool mayor Ned Mannoun welcomed the funding but warned against promising the region incomplete projects.

"Today we merely bought land. Nothing about when the job will be finished nor who will fund it - which we estimate at $10 billion - at today's prices.

"The longer it goes, the more expensive it gets," he said.

The announced extension addressed a "missing link" in western Sydney, the Property Council of Australia said.

But it warned further investment was needed to ensure an efficient and traveller-friendly rail network.

The existing heavy rail line between Leppington and Glenfield would need to be converted to metro to prevent unnecessary interchanges between the two networks, slowing down travel and limiting accessibility, the council's western Sydney regional director Ross Grove said.

Under-served by public transport, the southwest Sydney suburbs of Oran Park and Narellan are likely to receive new high-capacity stations as part of the future Bradfield to Macarthur line.