Treasury Secretary Steven Mnuchin said on Wednesday outgoing President Donald Trump supported a different Republican proposal put forth by Senate Majority Leader Mitch McConnell after McConnell on Tuesday rejected the bipartisan package.

No. 2 Senate Republican John Thune, however, told reporters the bipartisan plan represented "progress" and "I think hopefully it'll be helpful in us getting a deal done".

House of Representatives Speaker Nancy Pelosi and Senate Democratic Leader Chuck Schumer urged McConnell, a Republican, to immediately engage in negotiations, using the $US908 billion ($A1.2 trillion) initiative as a foundation.

McConnell aides did not immediately comment.

McConnell's own outline is very close to the legislation the Senate leader has been touting for months and was rejected by Democrats, according to one Senate Republican source.

The plan is understood to include $US332.7 billion in new loans or grants to small businesses.

"The president will sign the McConnell proposal he put forward yesterday. We look forward to making progress on that," Mnuchin told reporters on Capitol Hill.

But Schumer blasted the Republican effort for excluding Democrats, who control the US House of Representatives.

"The Republican leader should not waste the Senate's time on another inadequate, partisan proposal and instead should sit down with Democrats to begin a true bipartisan effort to quickly meet the needs of the country," Schumer said.

He noted the McConnell proposal includes liability protection for businesses that Democrats reject.

Adding to the pressure, the two parties face a December 11 deadline to pass a $US1.4 trillion budget or risk a shutdown of the government as the COVID-19 crisis worsens across the United States.

Senate Appropriations Committee Chairman Richard Shelby has raised the possibility that a short-term extension of existing funds might be needed if there is no deal by December 11.

Australian Associated Press