US Senate Republicans have crushed a Democratic blockade of President Donald Trump's Supreme Court nominee in a fierce partisan brawl, approving a rule change dubbed the "nuclear option" to allow conservative judge Neil Gorsuch's confirmation by Friday.

With ideological control of the nation's highest court at stake, the Republican-led Senate voted 52-48 along party lines on Thursday to change its long-standing rules in order to prohibit a procedural tactic called a filibuster against Supreme Court nominees.

That came after Republicans failed by a 55-45 tally to muster the 60-vote super-majority needed to end the Democratic filibuster that had sought to deny Gorsuch confirmation to the lifetime post.

The Senate paved the way for senators to confirm Gorsuch by simple majority. Republicans control the Senate 52-48.

The rule change has been dubbed the "nuclear option" because it has been considered an extreme break with Senate traditions, and Trump has encouraged Republican Senate Majority Leader Mitch McConnell to "go nuclear".

"This will be the first and last partisan filibuster of the Supreme Court," McConnell said on the Senate floor, accusing Democrats of trying to inflict political damage on Trump and to keep more conservatives from joining the high court.

Senate Democratic leader Chuck Schumer said the move had "irrevocably" taken the Senate away from its founding principles.

"In 20 or 30 or 40 years, we will sadly point to today as a turning point in the history of the Senate and the Supreme Court, a day when we irrevocably moved further away from the principles our founders intended for these institutions: principles of bipartisanship, moderation and consensus," he said.

Schumer ridiculed McConnell's contention that the Democratic action was unprecedented, noting the Republican-led Senate last year refused to consider former president Barack Obama's nomination of appellate judge Merrick Garland for the same high court seat that Trump elected Gorsuch to fill.

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Senate confirmation of Gorsuch, 49, would restore the nine-seat court's 5-4 conservative majority, enable Trump to leave an indelible mark on America's highest judicial body, and fulfill a top campaign promise by the Republican president. Gorsuch could be expected to serve for decades.

With the failure of Republican healthcare legislation in Congress and with federal courts blocking the president's ban on people from several Muslim-majority nations from entering the US, securing Gorsuch's confirmation took on even greater importance for Trump, who took office in January.

The court's ideological leaning could help determine the outcome of cases involving the death penalty, abortion, gun control, environmental regulations, transgender rights, voting rights, immigration, religious liberty, presidential powers and more.

The nine-seat Supreme Court has had a vacancy since conservative Justice Antonin Scalia died in February 2016.

Liberal groups called for an all-out fight to reject Gorsuch, a staunch conservative who is likely to vote "to limit gay rights, uphold restrictions on abortion, and invalidate affirmative action programmes", according to a study that analyses the ideologies of potential Supreme Court nominees.

Senators on both sides of the aisle lamented the trajectory they were on toward the Senate rules change, though they themselves were in position to prevent it from happening and failed to do so.

Moderate Republican Senator Susan Collins of Maine said roughly 10 senators from both parties worked over the weekend to come up with a deal to stave off the so-called nuclear option, but couldn't come to agreement.

In 2005, a bipartisan deal headed off Republican plans to remove the filibuster barrier for lower-court nominees, but in 2013 Democrats took the step, leaving the filibuster in place only for Supreme Court justices.

And now it too is gone. For now the filibuster barrier on legislation will remain, though many fear it could be the next to go.

"I fear that someday we will regret what we are about to do. In fact, I am confident we will," said Republican Senator John McCain. "It is imperative we have a functioning Senate where the rights of the minority are protected regardless of which party is in power at the time."

Nonetheless, McCain voted with McConnell on the rules change, saying he felt he had no choice.

Republicans have called Gorsuch superbly qualified and one of the most distinguished appellate judges on the bench, and they blamed the Democrats for politicising the confirmation process.

Democrats accused Gorsuch of being so conservative as to be outside the judicial mainstream, favouring corporate interests over ordinary Americans in legal opinions, and displaying insufficient independence from Trump.