Prime Minister Scott Morrison on Monday said the metro line would be complete and operational when the under-construction airport is inaugurated in 2026.

Preliminary construction begins this year and major works start in 2021.

The metro line will run to St Marys train station, to the airport's north, via Luddenham and Orchard Hills. A trip from Western Sydney Airport to St Marys will take about 15 minutes.

Commuters would then have to switch to the existing train network for onward travel to Parramatta or the Sydney CBD.

The metro trains would be single-deck and driverless.

The federal and NSW governments will each tip in $1.75 billion to expedite construction of the metro, with Canberra taking up the cost burden in the project's early stages. The whole project will cost about $11 billion, dependent on geotechnical assessments.

"You can see it all happening - this is how Australia makes its way back out of the COVID-19 crisis," Mr Morrison told reporters on Monday.

"These are job-making investments - when I talk about a JobMaker program, it's through projects like this, about the partnerships we're bringing together."

Mr Morrison said the government would continue looking to expedite infrastructure projects amid the COVID-19 pandemic.

Premier Gladys Berejiklian said the metro project would create 14,000 jobs over the next six years, which she said was "music to her ears".

"We know we have a job ahead of us of getting people into work, into sustainable jobs. Having those direct and indirect jobs is fantastic," Ms Berejiklian told reporters on Monday.

The construction of the airport at Badgerys Creek is projected to cost $5.3 billion.

Australian Associated Press