WASHINGTON, Sep 30 (AFP) - US Congress approved a stopgap funding Bill on Thursday (Sep 30) in a rare show of cross-party unity to avert a crippling government shutdown, as Democratic leaders struggle to overcome fierce infighting over President Joe Biden's domestic agenda.

Hours ahead of the midnight deadline, the House of Representatives voted to keep the lights on until Dec 3 with a resolution that had already advanced comfortably from the Senate, with opposition Republicans supporting the ruling Democrats in both chambers.

"This is a good outcome, one I'm happy we are getting done," Chuck Schumer, the top Democratic senator, told colleagues on the chamber floor ahead of both votes, which were never in serious doubt.

"With so many things to take care of here in Washington, the last thing the American people need is for the government to grind to a halt."

The rare example of bipartisan cooperation comes with Democratic leaders trying to hammer out a deal over Biden's faltering US$3.5 trillion social spending package, which has no Republican support, and a bipartisan US$1 trillion infrastructure Bill.

Democratic progressives and moderates are entrenched in a war of words over the programmes, as Republicans enjoy the disarray from the sidelines with one eye on next year's midterm elections.

The Senate-passed bipartisan infrastructure Bill is due for a crucial vote in the House on Thursday that appears to have no chance of passing, with the Democrats' left wing in open revolt.

The progressives don't trust that centrists, who object to the size and scope of the larger spending package, will honour an agreement to pass the legislation once infrastructure is across the line.

West Virginia's Senator Joe Manchin inflamed tensions Wednesday with a statement arguing that trillions of dollars in extra spending was "fiscal insanity", solidifying opposition to the smaller infrastructure Bill.

He told reporters on Thursday that he was unwilling to go above US$1.5 trillion.