Pressure is mounting on the federal government to consider funding all or part of a rail line to the Badgerys Creek airport site.

The country's largest airline and the Baird government both made representations on Friday for public transport to run to the airport when it opens in the middle of the next decade.

The federal government has committed $3.6 billion for an infrastructure package to support the airport site, the bulk of which would be used on road upgrades around south-west Sydney.

"The government's focus is roads first and airport second," Prime MinisterTony Abbott said in a prerecorded statement to a conference on Friday, organised to support a Badgerys Creek airport.

But the government has committed only to reserve space for a future rail line to the airport, saying a rail tunnel and station cavity would be dug into the site as part of earthworks preparation.

The train line, which would be an extension of the existing south-west rail link to Leppington, would not be running when the airport is scheduled to open, some time around 2026.

At the conference on Friday, organised by the Sydney Business Chamber, chief executive officer at Jetstar Australia and New Zealand David Hall said building the airport's future would hinge on supporting infrastructure.

"It is infrastructure that will determine whether western Sydney is positioned for success or if that's left to chance."

He said the airport needed to be run without a curfew, in contrast to Sydney's existing airport at Mascot, and that the new site needed to be easy to access.

"All global evidence would suggest that this airport will need greater road and rail links from day one if it is to sustain commercial levels of demand," Mr Hall said.

Mr Hall made it clear that he was speaking on behalf of the Qantas Group, which owns Jetstar.

NSW Transport Minister Andrew Constance said "all things should be considered" in relation to infrastructure around the airport.

"I certainly would like to see ways in which we can co-operate with the feds around public transport infrastructure in particular," Mr Constance told Fairfax Media.

"I think it is a case of putting all things on the table," he said.

"We must recognise the enormous contribution from the Commonwealth when it comes to roads development.

"If there's any way that they can give consideration to supporting the state in terms of some of that public transport infrastructure around Badgerys Creek, that would be terrific if they could."

The conference heard from US airport expert John Kasarda, who proposed the radical notion of building a massive airport "mega-hub" at Badgerys Creek by either diminishing or closing Sydney's existing Mascot Airport.

Dr Kasarda, the author of a book called Aerotropolis, said Sydney and Australia needed a larger facility than was possible to construct at Mascot.

"Sydney and the nation deserve no less than a 21st-century, state of the art airport," Dr Kasarda said.

He proposed two means of creating this sort of airport at Badgerys Creek.

The first was restricting the Kingsford Smith Airport at Mascot to domestic, business-oriented flights, ensuring that there would be sufficient demand at Badgerys Creek.

The second was closing Kingsford Smith and using the funds raised to build a much more substantial airport in Sydney's West.

Dr Kasarda said the site would be a "gold mine" that could be "used to generate a truly 21st-century megahub."

The director of the Sydney Business Chamber, David Borger, said it was a "bold new idea, well worth considering." "It's time we thought bigger," Mr Borger said.

Kerrie Mather, chief executive of Sydney Airport Corporation, which holds the first right to build and operate an airport at Badgerys Creek, also addressed the conference.

Ms Mather said Sydney Airport was "100 per cent committed" to the consultation process with government, and said two-thirds of the world's busiest airports shared their catchment areas with other major facilities.

The majority of these, about 77 per cent, shared common ownership between the two airports.

"We believe a western Sydney airport has the opportunity to be something very special," Ms Mather said, while also adding that the airport needed to be run without a curfew.

The federal government has said the airport would not have a flight curfew, while the state Labor opposition has said that it should. Mr Constance said the operating pattern of the airport was a matter for the Commonwealth, but added that it must "maximise the economic and social opportunities for the people of NSW."

Labor insists that a train line should be running to Badgerys Creek when the airport is opened, though it has said the bulk of the funding should come from the private sector.