Confidential plans for Sydney's second airport at Badgerys Creek have revealed construction could begin next year on a facility that could eventually double the size and passenger capacity of Sydney's present airport at Mascot.

The plans show the first stage of the airport would include a single east-west runway of 3.7 kilometres and a small terminal servicing international and domestic flights, as well as a cargo terminal. Slated to be completed within eight years at a cost of about $4 billion, the first stage would deliver an airport capable of servicing 10 million passengers a year.

Construction of the new airport at Badgerys Creek could start next year. Credit:Brendon Thorne

But plans for the airport's final configuration, obtained by News Corp Australia, reveal a design that could eventually rival the size and capacity of the present JFK International Airport in New York.

By 2050, the Badgerys Creek airport plans include twin parallel 3.7 kilometre runways, with passenger terminals positioned between them.