NSW Premier Barry O'Farrell has asked federal politicians to show him the money if they are so keen on a second airport for Sydney.

The premier has ruled out another airport in Sydney, instead backing an upgrade of Canberra airport and linking it to Sydney by a high-speed rail line.

Federal Transport Minister Anthony Albanese and opposition treasury spokesman Joe Hockey have both signalled support for a second Sydney airport.

Mr O'Farrell told Macquarie Radio on Wednesday that airports were federal projects and were federally controlled.

"It's about federal dollars; an airport would cost $7 billion to $11 billion," he said.

"I don't have that money. The money that I have will go into roads, railways, hospitals, schools; the infrastructure that people in this state elect us for."

The premier said he heard Mr Albanese and Mr Hockey constantly talking about the need for a second Sydney airport.

"But what I never hear from Joe Hockey, what I never hear from Anthony Albanese, is a commitment to put a single dollar towards building a project that in the next breath they claim is critical for Sydney and Australia.

"To quote Tom Cruise, 'Show me the money.'"

Mr O'Farrell said his government's approach was to make better use of Sydney Airport within the existing curfew to get more planes in and out.

He said if there were fast trains between Sydney and Canberra, it would open up more slots for flights at Kingsford Smith.