Millions of Americans are about to see their jobless benefits expire on Saturday as U.S. President Donald Trump has so far refused to sign into law a $2.3 trillion pandemic aid and spending package, insisting that it does not do enough to help ordinary people.

Trump stunned Republicans and Democrats alike when he said this week he was unhappy with the massive bill, which provides $892 billion in badly needed coronavirus relief, including extending special unemployment benefits expiring on December 26, and $1.4 trillion for normal government spending.

Without Trump's signature, about 14 million people could lose those extra benefits, according to Labor Department data. A partial government shutdown will begin on Tuesday unless Congress can agree on a stop-gap government funding bill before then.

After months of wrangling, Republicans and Democrats agreed to the package last weekend, with the support of the White House. Trump, who hands over power to Democratic President-elect Joe Biden on January 20, did not object to terms of the deal before Congress voted it through on Monday night.

But since then he has complained that the bill gives too much money to special interests, cultural projects and foreign aid, while its one-time $600 stimulus checks to millions of struggling Americans were too small. He has demanded that be raised to $2,000.

"I simply want to get our great people $2000, rather than the measly $600 that is now in the bill," the president tweeted on Saturday.

His refusal to sign prompted sharp rebuke from Biden, who called on the outgoing Republican president to act immediately.

"This abdication of responsibility has devastating consequences... This bill is critical. It needs to be signed into law now," said Biden, who is spending the holiday in his home state of Delaware.

Many economists agree the bill's aid is too low but say the immediate support is still welcome and urgently necessary as Americans face an unprecedented holiday season amid a pandemic that has killed nearly 330,000 people in the United States, with a daily death toll now repeatedly well over 3,000 people, the highest since the pandemic began.

Trump last week vetoed a $740 billion bill authorising the nation's defence programmes. On Monday, the House is scheduled to vote on overriding Mr Trump's veto. If the House vote succeeds, the Senate could hold its vote as early as Tuesday. Both chambers passed the defence spending bill with margins well over the two-thirds majority needed to override a veto.