The Republican-led Senate judiciary committee voted in favour of President Donald Trump's nomination of Amy Coney Barrett to a lifetime U.S. Supreme Court post on Thursday, with Democrats boycotting the proceedings after fiercely opposing her confirmation.

Calling it a "groundbreaking, historic moment," committee chair Lindsey Graham led the 22-member committee's approval with unified support among its 12 Republican members, even with the Democrats vowing to stay away.

Committee approval would pave the way for a final confirmation vote on the Senate floor planned by Republican Majority Leader Mitch McConnell for Monday.

The confirmation of Barrett, a federal appeals court judge, would expand the top U.S. judicial body's conservative majority to 6-3 if approved by the full chamber.

In announcing their boycott of Thursday's vote, Senate Democratic leader Chuck Schumer and judiciary committee Democrats said of Barrett's nomination: "This has been a sham process from the beginning."

Democrats said they "will not grant this process any further legitimacy by participating" in the committee's vote just 12 days before the U.S. presidential election between Trump and Democrat Joe Biden in which tens of millions of ballots have already been cast.

"We're not going to allow them to take over the committee," Graham said Thursday of the Democrats.

Texas Republican John Cornyn called it a "surreal environment," given the Democratic no-show.

Trump nominated Barrett to succeed the late liberal Justice Ruth Bader Ginsburg.

Mike Davis, a former top aide on the panel who now advises Senate Republicans, said the committee was well within its normal practice to hold the vote, even with Democrats skipping it. He said the longstanding practice has been to allow business to go forward if all members of the majority, Republicans, attend.

Countering that view, a Democratic aide granted anonymity to discuss the proceedings said never before have the rules been brushed past for a Supreme Court confirmation.

Democrats fill seats with placards

Barrett would be the fifth woman on the top court but given her past record, by far the most conservative.

Sandra Day O'Connor, the first, was seen as a moderate conservative, while the three subsequent female justices have been liberal.

Committee chair Lindsey Graham is seen presiding on a TV monitor between images of Americans helped by the Affordable Care Act (ACA), according to Democrats. (Hannah McKay/Reuters)

A favourite of Christian conservatives, Barrett frustrated committee Democrats during her confirmation hearing last week by sidestepping questions on abortion, presidential powers, climate change, voting rights, Obamacare and other issues.

Seats that would have been occupied by Senate Democrats were filled Thursday with blown-up placards of American citizens the party says will be stripped of Obamacare coverage if the top court rules after a hearing to be held soon after the election to void aspects of what is known as the Affordable Care Health Act.

The 48-year-old Barrett is a devout Catholic who personally opposes abortion. Barrett told the committee last week that she believed the landmark 1973 Roe v. Wade ruling legalizing abortion nationwide was not a "super-precedent" that could never potentially be overturned. Barrett also said she had "no agenda" to roll back abortion rights.

Trump said in 2016 he would appoint justices who would overturn Roe. Senate Republicans, who have made confirmation of Trump's conservative judicial appointees a high priority, have pulled out all the stops to ensure that the chamber can confirm Barrett to the post before the election on Nov. 3, as the president has requested.

Senate approval all but guaranteed

Republicans hold a 53-47 Senate majority, making her confirmation a virtual certainty. Trump has said he believes the Supreme Court will decide the election's outcome and has made clear that he wants Barrett on the bench for any election-related cases.

Democrats pressed her to recuse herself from such cases because of a conflict of interest in potentially deciding the political fate of the president who nominated her so close to the election. She rebuffed their pleas.

WATCH | Graham, Schumer comment on Thursday's committee vote:

Graham and Schumer speak on U.S. Senate judiciary committee vote

38 minutes ago

1:40

U.S. Senate judiciary committee chair Lindsey Graham said the committee vote is a 'historic moment' for American politics, in contrast to Senate minority leader Chuck Schumer, who said the nomination of Amy Coney Barrett is the most 'illegitimate' process he has seen. 1:40

No nominee to the Supreme Court has ever been confirmed by the Senate this close to a presidential election. Democrats were incensed that Senate Republicans moved forward with the nomination so near an election after refusing in 2016 to allow the chamber to act on a Supreme Court nomination by Trump's Democratic predecessor, Barack Obama, because it was an election year.

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Some on the left have floated the idea of expanding the number of justices if Biden wins to counter the court's rightward drift in light of the actions of Senate Republicans in 2016 and now. Republicans have decried the idea as "court-packing."

Biden said last week he was "not a fan" of court-packing but has kept his options open. The number of justices has been fixed by law at nine for more than a century.

Trump appointed Barrett to the Chicago-based 7th U.S. Circuit Court of Appeals in 2017. If confirmed, Barrett could serve on the Supreme Court for decades, alongside Trump's two other appointees, Neil Gorsuch and Brett Kavanaugh.