A proposed high-speed rail line linking Los Angeles with the US gambling and entertainment capital Las Vegas moved closer to reality Tuesday with the announcement of a $3 billion government grant.

The cash will come from President Joe Biden's signature infrastructure bill aimed at revamping the country's creaking rails, roads and bridges, and is part of a plan to double the number of people taking the train by 2040.

When completed, the 218-mile trip between Las Vegas and downtown Los Angeles could take as little as 2 hours and 40 minutes, press reports said, half the current journey time by car.

While high speed rail is the norm in much of Europe and Asia, particularly in China and Japan, the United States has long lagged behind.

But there has been a renewed emphasis on projects like this as the United States hurries to green its polluting transport sector and encourage citizens out of their gas-guzzling cars.

A line linking Las Vegas with America's second biggest city has been mooted for almost two decades, during which time its proposed cost has ballooned.

The $3 billion grant announced Tuesday represents just a quarter of the price tag of the project to be built by Florida-based Brightline West, which press reports suggest could be up and running by 2028.

Nevada Senator Jacky Rosen said the line could reduce the number of cars making the journey by up to 3 million a year, slashing planet-warming carbon dioxide emissions by 400,000 tons annually.

"This historic high-speed rail project will be a game changer for Nevada's tourism economy and transportation," she said.

"It'll bring more visitors to our state, reduce traffic on the I-15 (highway), create thousands of good paying jobs, and decrease carbon emissions, all while relying on local union labor."

Wes Edens, chairman of Brightline, said the company was honored that the government had entrusted it with the project.

"This is a historic moment that will serve as a foundation for a new industry, and a remarkable project that will serve as the blueprint for how we can repeat this model throughout the country," he said.

"We're ready to get to work to bring our vision of American-made, American-built, world-class, state-of-the-art high speed train travel to America."

Biden is expected formally to announce the grant when he visits Las Vegas this week.

Last month the White House said there would be $16.4 billion in new funding for 25 passenger rail projects in the country's northeast.