Brett Kavanaugh’s Supreme Court seat looks all but confirmed after he won the backing of key senators despite an FBI investigation into sexual assault allegations.

Republican Senator Susan Collins and Joe Manchin, a Democrat, both indicated their backing for the judge on Friday, BBC reported.

Judge Kavanaugh’s confirmation would tilt America’s highest court in favour of conservatives.

The court has the final say on issues such as abortion and gun control.

A final vote on whether Judge Kavanaugh will join the nine-member panel is scheduled for Saturday. If confirmed, the position is for life.

Hours before the undecided senators indicated their backing, the US Senate narrowly advanced President Donald Trump’s nominee to a final vote by voting to strictly limit debate on the issue.

Friday’s “cloture” vote — 51-49 in favour — was a test of support for the embattled nominee who has faced allegations of sexual misconduct from three women, including Prof. Christine Blasey Ford.

Senator Collins ended hopes she would side with Democrats in the final vote, telling fellow senators she did not believe the “charges can fairly prevent Judge Kavanaugh from serving on the court”.

“The facts presented do not mean that Professor Ford was not sexually assaulted that night or at some other time but they do lead me to conclude that the allegations failed to meet the more likely than not standard,” she said.

Senator Manchin, who is up for re-election in West Virginia, a traditionally Republican state that Trump won by a landslide, told the Senate moments later he “found Judge Kavanaugh to be a qualified jurist who will follow the constitution and determine cases based on the legal findings before him”.

The reaction has been swift, with former President George Bush and White House Press Secretary Sarah Sanders both tweeting their support for Collins.

Manchin, however, has found himself in the firing line.

A liberal group which raises money for Democratic candidates, Priorities USA, immediately said it would not be giving any funds to his re-election campaign.

Outside, protesters shouted “shame on you” as Manchin spoke to reporters about his decision.

Meanwhile, a tweet asking someone to run for Senator Collins’s seat in Maine when it comes up for re-election in 2020 from former White House communication chief, Jen Psaki, had a swift response from former UN ambassador Susan Rice.

She later clarified she was “not making any announcements” but was “deeply disappointed in Senator Collins’s vote for Kavanaugh”.