The Prime Minister has pledged up to $5 billion to help build the long-awaited rail link from Melbourne Airport to the CBD.

Key points: The "time for talk is over," Malcolm Turnbull says

The "time for talk is over," Malcolm Turnbull says The PM wants the Victorian Government to match its pledge

The PM wants the Victorian Government to match its pledge Last year, the Victorian Government said it wanted to build the rail link within a decade

A Melbourne Airport train line has been debated and planned for decades, but Malcolm Turnbull has declared his funding promise will ensure it becomes a reality.

"The time for talk is over. There have been countless reviews, reports and recommendations but Melbourne is still waiting for a service almost all of the world's great cities take for granted," Mr Turnbull said.

"This is the rail link that Melbourne, Victoria and the millions of people who use the airport every year demand and deserve."

Proposed routes for the Melbourne Airport rail link. ( ABC News )

While the funding announcement is significant, the $5 billion pledged will not be enough to cover the entire cost of the project.

Mr Turnbull will today ratchet up pressure on the Victorian Government to make a matching commitment and pour in another $5 billion.

Possible routes: Craigieburn Link: Would follow existing Craigieburn line before turning off at Broadmeadows

Would follow existing Craigieburn line before turning off at Broadmeadows Albion East Link: Would take Metro Tunnel and Sunbury line to Sunshine before turning off for airport

Would take Metro Tunnel and Sunbury line to Sunshine before turning off for airport Flemington Link: Would travel through Flemington and Kensington with new stops in Maribyrnong

Would travel through Flemington and Kensington with new stops in Maribyrnong Direct Tunnel Link: Would take a tunnel from Footscray to Maribyrnong with new stops at Victoria University and in Maribyrnong

Last year, the Victorian Andrews Government announced it wanted to build an airport rail link within a decade.

"We're already committed to a rail link to the airport and we're obviously happy to work with any Commonwealth Government on this project," Victoria's Minister for Public Transport, Jacinta Allan, said in response to the Turnbull Government announcement.

"It's good the Prime Minister has finally found Victoria on a map, and we'll accept this funding given how much he short-changes our state."

Interviewed on ABC Radio Melbourne on Thursday, Treasurer Scott Morrison said the $5 billion for the airport link would be "the single biggest announcement I'll be making in this year's budget on infrastructure".

"This brings to over $17 billion our commitments to infrastructure here in Victoria," Mr Morrison said.

The Coalition has already committed $30m to put together a business case for the rail line. ( Supplied, file photo )

Ms Allan said Victoria's plan for an airport rail link included fast rail to the regions and it was "concerning" that only one of four possible routes proposed by the Commonwealth would allow for this.

The Victorian Government says it wants the airport link to "untangle" regional and metropolitan rail services, arguing boosting regional services would maximise the benefits of the link and ensure it did not simply become an "expensive funnel" between the airport and CBD.

The Federal Government has not committed to that idea, but it has not yet ruled it out either.

Congestion has been steadily worsening in Melbourne, and the Prime Minister said building the link would "slash travel times, bust congestion, boost the Victorian economy and create thousands of new jobs".

"We are under no illusion that such a city-shaping project does not come cheap. That is why we are making such a significant commitment," Mr Turnbull said.

"We want the Victorian Government to partner with us in a true 50:50 funding partnership to build and own this iconic piece of infrastructure. We also welcome the involvement of the private sector."

The Coalition has already committed $30 million to put together a business case for the rail line — and Mr Turnbull said that would provide a clearer picture of the best route, as well as the project's final price tag.

Victorian Liberal leader Matthew Guy was quick to pounce on the announcement.

"$5 billion! If the Andrews Govt won't build an airport rail link, it's outstanding to see the federal Liberal National government will," he said on Twitter.