Millions of Americans saw their jobless benefits expire on Saturday after US President Donald Trump refused to sign into law a $US2.3 trillion ($A3 trillion) pandemic aid and spending package, protesting that it did not do enough to help everyday people.

Trump stunned Republicans and Democrats alike when he said this week he was unhappy with the massive bill, which provides $US892 billion ($A1.2 trillion) in badly needed coronavirus relief.

This includes extending special unemployment benefits expiring on December 26, and $US1.4 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 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 $US600 ($A790) stimulus cheques to millions of struggling Americans were too small.

He has demanded that be raised to $US2,000 ($A2,632).

“Why would politicians not want to give people $2,000, rather than only $600?…Give our people the money!” the billionaire president tweeted on Christmas Day, much of which he spent golfing at his Mar-a-Lago resort in Palm Beach, Florida.

Many economists agree the bill’s aid is too low but say the immediate support is still welcome and necessary.

A source familiar with the situation said Trump’s objection to the bill caught many White House officials by surprise.

While the outgoing president’s strategy for the bill remains unclear, he has not vetoed it and could still sign it in coming days.

On Saturday, he was scheduled to remain in Mar-a-Lago, where the bill has been sent and awaits his decision.

Biden, whose November 3 electoral victory Trump refuses to acknowledge, is spending the holiday in his home state of Delaware and had no public events scheduled for Saturday.

-AAP