US President Donald Trump's tax-cut package cleared its final hurdle in the US Congress on Thursday, as the Republican-controlled House of Representatives narrowly approved the massive bill and sent it to him to sign into law.

The 218-214 vote amounts to a significant victory for the Republican president that will fund his immigration crackdown, make his 2017 tax cuts permanent and deliver new tax breaks that he promised during his 2024 campaign.

It also cuts health and food safety net programs and zeroes out dozens of green energy incentives.

It would add US$3.4 trillion to the nation's US$36.2 trillion debt, according to the nonpartisan Congressional Budget Office.

Despite concerns within Trump's party over the 869-page bill's price tag and its hit to healthcare programs, in the end just two of the House's 220 Republicans voting against it, following an overnight standoff.

The bill has already cleared the Republican-controlled Senate by the narrowest possible margin.

The White House said Trump will sign it into law at 2100 GMT on Friday, the July 4 Independence Day holiday.

Republicans said the legislation will lower taxes for Americans across the income spectrum and spur economic growth.

Trump said his signature bill would boost the US economy.

"It's going to make this country into a rocket ship," Trump told reporters as he headed for a rally in Iowa to kick off America's 250th birthday celebrations, calling it the "the biggest bill of its kind ever signed."

"This is jet fuel for the economy, and all boats are going to rise," House Speaker Mike Johnson said.

Every Democrat in Congress voted against it, blasting the bill as a giveaway to the wealthy that would leave millions uninsured.

"The focus of this bill, the justification for all of the cuts that will hurt everyday Americans, is to provide massive tax breaks for billionaires," House Democratic Leader Hakeem Jeffries said in an eight-hour, 46-minute speech that was the longest in the chamber's history.

Though roughly a dozen House Republicans threatened to vote against the bill, only two ended up doing so: Brian Fitzpatrick of Pennsylvania, a centrist, and Thomas Massie of Kentucky, a conservative who said it did not cut spending enough.

Republicans raced to meet Trump's July 4 deadline, working through last weekend and holding all-night debates in the House and the Senate.

The bill passed the Senate on Tuesday in a 51-50 vote in that saw Vice President JD Vance cast the tiebreaking vote.

According to the CBO, the bill would lower tax revenues by US$4.5 trillion over 10 years and cut spending by US$1.1 trillion. Those spending cuts largely come from Medicaid, the health program that covers 71 million low-income Americans.

The bill would tighten enrollment standards, institute a work requirement and clamp down on a funding mechanism used by states to boost federal payments – changes that would leave nearly 12 million people uninsured, according to the CBO.

Nonpartisan analysts have found that the wealthiest Americans would see the biggest benefits from the bill, while lower-income people would effectively see their incomes drop as the safety-net cuts would outweigh their tax cuts.

The increased debt load created by the bill would also effectively transfer money from younger to older generations, analysts say. (Agencies)