A spending bill backed by Donald Trump has failed in the US House of Representatives as dozens of Republicans defied the president-elect, leaving Congress with no clear plan to avert a fast-approaching government shutdown that could disrupt Christmas travel.

The vote laid bare fault lines in Trump's Republican Party that could surface again next year when they control the White House and both chambers of Congress.

Trump had pressured lawmakers to tie up loose ends before he takes office on January 20, but members of the party's right flank refused to support a package that would increase spending and clear the way for a plan that would add trillions more to the federal government's $36 trillion in debt.

"I am absolutely sickened by a party that campaigns on fiscal responsibility and has the temerity to go to the American people and say you think this is fiscally responsible," said Republican Representative Chip Roy.

Roy was one of 38 Republicans who voted against the bill.

The package failed by a vote of 174-235 just hours after it was hastily assembled by Republican leaders seeking to comply with Trump's demands.

A prior bipartisan deal was scuttled after Trump and the world's richest person Elon Musk came out against it a day earlier.

Republican House Speaker Mike Johnson provided no details when reporters asked him about next steps after the failed vote.

"We will come up with another solution," he said.

Government funding is due to expire at midnight on Friday. If lawmakers fail to extend that deadline, the US government will begin a partial shutdown that would interrupt funding for everything from border enforcement to national parks and cut off paycheques for more than 2 million federal workers.

The US Transportation Security Administration warned that travellers during the busy holiday season could face long lines at airports.

The bill that failed largely resembled the earlier version that Musk and Trump had blasted as a wasteful giveaway to Democrats.

It would have extended government funding into March and provided $100 billion in disaster relief and suspended the debt.

Republicans dropped other elements that had been included in the original package, such as a payrise for lawmakers and new rules for pharmacy benefit managers.

At Trump's urging, the new version also would have suspended limits on the national debt for two years – a manoeuvre that would make it easier to pass the dramatic tax cuts he has promised.

Johnson before the vote told reporters that the package would avoid disruption, tie up loose ends and make it easier for lawmakers to cut spending by hundreds of billions of dollars when Trump takes office next year.

"Government is too big, it does too many things, and it does few things well," he said.

Democrats blasted the bill as a cover for a budget-busting tax cut that would largely benefit wealthy backers such as Musk, while saddling the country with trillions of dollars in additional debt.

"How dare you lecture America about fiscal responsibility, ever?" House Democratic Leader Hakeem Jeffries said during floor debate.

Even if the bill had passed the House, it would have faced long odds in the Senate, which is currently controlled by Democrats.

The White House said Democratic President Joe Biden did not support it.

Previous fights over the debt ceiling have spooked financial markets, as a US government default would send credit shocks around the world.

The limit has been suspended under an agreement that technically expires on January 1, though lawmakers likely will not have to tackle the issue before the spring.

When he returns to office, Trump aims to enact tax cuts that could reduce revenues by $8 trillion over 10 years, which would drive the debt higher without offsetting spending cuts.

He has vowed not to reduce retirement and health benefits for seniors that make up a vast chunk of the budget and are projected to grow dramatically in the years to come.

The last government shutdown took place in December 2018 and January 2019 during Trump's first White House term.

The unrest also threatened to topple Johnson, a mild-mannered Louisianan who was thrust unexpectedly into the speaker's office last year after the party's right flank voted out then-Speaker Kevin McCarthy over a government funding bill.

Johnson has repeatedly had to turn to Democrats for help in passing legislation when he has been unable to deliver the votes from his own party.

He tried the same manoeuvre with the latest vote, but this time fell short.

Several Republicans said they would not vote for Johnson as speaker when Congress returns in January, potentially setting up another tumultuous leadership battle in the weeks before Trump takes office.

What to know about the debt ceiling debate

What is the debt ceiling?

The debt ceiling, or debt limit, is the total amount of money that the United States government can borrow to meet its existing legal obligations. For the Treasury Department to borrow above that amount, the limit must be raised by Congress.

The federal debt stands at roughly $36 trillion, and the spike in inflation after the coronavirus pandemic has pushed up the government's borrowing costs such that debt service next year will exceed spending on national security.

The last time lawmakers raised the debt limit was June 2023. Rather than raise the limit by a dollar amount, lawmakers suspended the debt limit through January 1, 2025. At that point, the limit will be automatically raised to match the amount of debt that has been issued by the Treasury Department.

The debt limit vote in recent times has been used as a political leverage point, a must-pass bill that can be loaded up with other priorities.

What is the debt ceiling fight all about?

Trump has tied a demand for dealing with the debt ceiling to the dispute over government funding, saying one should not be addressed without the other.

When he rejected the spending proposal, Trump said that he wanted the debt ceiling debate settled before he takes office next month.

Warning of trouble ahead for Johnson and Republicans in Congress, Trump said, "Anybody that supports a bill that doesn't take care of the Democrat quicksand known as the debt ceiling should be primaried and disposed of as quickly as possible."

What happens if the debt ceiling isn't raised?

There's actually no need to raise the debt limit right now. On January 1, when the debt limit is triggered, the Treasury Department can begin using what it calls "extraordinary measures" to ensure that America doesn't default on its debts.

Some estimate these accounting manoeuvres could push the default deadline to the summer of 2025 – but that's exactly what Trump wants to avoid, since an increase would then be needed while he is president.

Lawmakers have always raised the debt ceiling in time because the consequences of failure are stark.

Without action, the government would go into default on its debts, a first-ever situation that Treasury Secretary Janet Yellen and economic experts have said could be "catastrophic" for the economy and global markets.

Raising or suspending the debt limit does not authorise new spending or tax cuts; it merely acknowledges past budgetary decisions – that is, current budget law – and so allows the federal government to meet its existing legal obligations.

For that reason and others, some have advocated doing away with the limit altogether.

What could the debt ceiling fight mean for Speaker Mike Johnson?

Dealing with the debt ceiling could have ramifications for Johnson, as he angles to keep his job in the new Congress that begins on January 3.

Trump said that Johnson would "easily remain speaker" for the next Congress if he "acts decisively and tough" in coming up with a new plan to also increase the debt limit, a stunning request just before the Christmas holidays that has put the beleaguered speaker in a bind.

The last House speaker, Kevin McCarthy, worked for months with President Joe Biden to raise the debt limit.

Even though they struck a bipartisan deal that cut spending in exchange for additional borrowing capacity, House Republicans said it didn't go far enough, and it ended up costing McCarthy his job.

Now, Trump is looking for Johnson to pass a debt ceiling extension just hours before a partial government shutdown.

What are Democrats saying about the debt ceiling debate?

After meeting with his caucus, Democratic Leader Hakeem Jeffries rejected any possibility that his members would bail out Republicans as the shutdown threat looms.

"GOP extremists want House Democrats to raise the debt ceiling so that House Republicans can lower the amount of your Social Security check," Jeffries said. "Hard pass."

Jeffries and other Democrats say Republicans should honour the spending agreement that was negotiated before Trump got involved. He called the new GOP plan "laughable".