WASHINGTON (REUTERS) - US Senate Republicans said on Friday (Dec 1) they had gathered the votes needed to pass a sweeping tax overhaul, after last-minute negotiations to ease some senators' concerns about the Bill's impact on the federal deficit, health care and property taxes.

On the brink of securing a badly needed victory, Senate Republican leader Mitch McConnell told reporters as he emerged from a morning meeting with colleagues: "We have the votes."

No formal text of the Bill - still very much a work in progress - had been released just hours before a final vote, which was expected later on Friday.

If approved, the Senate and the House of Representatives, which already has passed its own tax Bill, would work together to craft a single measure to send to the White House for enactment.

President Donald Trump, who has played largely a cheerleading role in the tax debate, strongly backs tax cuts and was expected to sign a Bill sent to him by the US Congress.

Five Republican senators whose commitments had been in doubt announced on Friday they would back the Bill: Steve Daines, Ron Johnson, Jeff Flake, James Lankford and Jerry Moran.

Senators Bob Corker and Susan Collins were the last holdouts as of mid-afternoon. Republican leaders said they were confident Collins would sign on eventually.

Details were sketchy but lawmakers said on Friday changes were being made to provisions dealing with the federal deduction for state and local property tax, a cut in the corporate income tax rate, the alternative minimum tax and a one-time tax on foreign profits held offshore by multinational corporations.

Gaining the support of the five additional senators gave the Republicans at least the 50 votes needed to pass the measure. Republicans hold a 52-48 majority over Democrats in the Senate and have Vice-President Mike Pence to break any tie votes.

Democrats have been united in their opposition to the Bill, calling it a giveaway to the wealthy and corporations.

"In the waning hours, this Bill is tilting further towards businesses and away from families," Senate Democratic leader Chuck Schumer said in a statement.

"Every time the choice is between corporations and families, the Republicans choose corporations.

"Today may be the first day of a new Republican Party - one that raises taxes on the middle class."

PRAISE FROM TRUMP

Trump, still looking for the first major legislative accomplishment of his presidency, praised fellow Republicans in Congress for their work in a Friday morning tweet and blamed Democrats for trying to derail the Bill.

Led by McConnell and with Trump deeply involved, Republicans in July failed to dismantle the Obamacare health law after years of attacking the signature achievement of former Democratic President Barack Obama. That embarrassing debacle damaged McConnell's reputation and infuriated Trump.

The Republican tax Bill would represent the biggest overhaul of the US tax system since the 1980s. Its success is seen by Republicans as crucial to their hopes of retaining control of Congress in the November 2018 elections.

Daines and Johnson announced their support for the Bill on Friday after winning more tax relief for non-corporate pass-through businesses. These include partnerships and other companies not organised as public corporations, encompassing most American business enterprises from mom-and-pop concerns to large financial and real estate organisations.

The Bill now features a 23 per cent tax deduction for such business owners, up from the original 17.4 per cent, according to statements from both senators.

In a statement, Flake said he had secured two objectives - eliminating an US$85 billion "expensing budget gimmick" in the measure and winning a commitment to work with him on fair and permanent protections for illegal immigrants who came to the United States as children.

Republicans also had been searching for a way to get Corker, a deficit hawk, on board. The legislation stalled late on Thursday when Senate rules prohibited adding a deficit-focused mechanism Corker had sought to add to the Bill.

Collins said she had won an agreement to change the Senate bill so state and local property taxes would be deductible up to US$10,000, mirroring legislation already passed by the House.

Collins also had pushed for concessions to minimise the impact on older and sicker Americans of a provision of the Bill that would repeal part of the Obamacare health law.