PM pledges train to Badgerys Creek airport

Prime Minister Malcolm Turnbull has backed plans for a fast train between Sydney and its second airport at Badgerys Creek, saying he hopes it will be ready when the airport opens in the mid 2020s.

Mr Turnbull has not revealed a dollar figure for any rail projects or who would fund the train line to the western Sydney airport.

"There is too little known about the route, the cost, the value created and the sources of funding," he told delegates at the Western Sydney Ideas Summit on Friday.

It was also too early to commit to a fully-functioning rail line by the time the airport is ready in 2026, he said.

"We are already setting aside space for rail including station boxes and approaches so that the rail link can be established whether at the time the airport opens, which would be preferable, or later."

Traffic forecasts show there won't be a demand for a rail link until the 2040s, Mr Turnbull said.

The federal government has already committed $2.9 billion in new roads spending to support the construction of a new airport, along with $700 million from the state government for a western Sydney road network.

The airport is expected to cater for an estimated 10 million passengers a year by 2030 and there are no plans for a curfew like its Sydney counterpart.

The promise comes as other leaders met at Friday's summit in Rydalmere, with keynote addresses from NSW Premier Mike Baird, Opposition Leader Luke Foley and head of the Greater Sydney Commission Lucy Turnbull.

Mr Baird said the airport couldn't be built without a rail link and he welcomed the announcement.

"What the prime minister has outlined is an intent to support that project. There's a lot more hard work that has to be done," he told reporters on Friday.

"Of course as a state premier I'd welcome any cheque that came with it."

Federal opposition infrastructure spokesman Anthony Albanese says if the airport is to be a success, it needs to be more than just runways and a terminal.

"Saying that you want a rail line to Badgerys Creek airport without providing any funding, without providing any clear step forward and without a commitment even that it will be completed in 10 years' time, is pretty inadequate," Mr Albanese told reporters in Sydney on Friday.

Tourism & Transport Forum CEO Margy Osmond says she isn't worried about funding yet because the rail line needed to be discussed further, including whether it will run with stops through western Sydney or connect express to Sydney first.

"We're looking at a hitchhikers' airport without the rail line," she said.