WASHINGTON - The US Senate on Saturday narrowly confirmed President Donald Trump's Supreme Court pick Brett Kavanaugh in its final floor vote, following a fierce partisan fight over sexual misconduct allegations against the nominee.

The confirmation appeared to secure a solid majority of conservatives on the US highest court in the coming years, a big win for Trump and the Republican Party.

Moments after the vote by 50 to 48, Trump tweeted that he will sign the Commission of Appointment later on Saturday so that the judge will be officially sworn in.

"Very exciting!" the president tweeted.

During the voting, hundreds of protesters were demonstrating on Capitol Hill, chanting "November is coming" and "We believe survivors".

"Vote them out," the demonstrators shouted.

Kavanaugh's confirmation is a major boost to Senate Republican candidates in upcoming midterm elections to be held on Nov 6, Senate Majority Leader Mitch McConnell said on Saturday.

The top Senate Republican said that partisan fights over Kavanaugh have revved up Republican voters across red states.

"Our base is on fire," McConnell said in an interview with The Hill news daily.

Meanwhile, Democrats also say their voters are now more fired up than ever to deliver a rebuke to the Republicans in the upcoming midterm elections, citing women's anger as a force.

Many fear that the confirmation of a highly controversial Kavanaugh may further divide the whole country and damage the Supreme Court's independent image.

Three women came forward last month to accuse Kavanaugh of sexually assaulting or harassing them during his high school and university years. Kavanaugh has denied all the accusations.

The 53-year-old federal appeals court judge will succeed Supreme Court Justice Anthony Kennedy, who retired on July 31 as a moderate and pivotal swing vote between conservatives and liberals on the nine-member bench.

The nine-member Supreme Court decides matters that shape the country's politics. It is both the highest appeals panel and a constitutional court.

Nominating Kavanaugh was the second time in two years that Trump has made a Supreme Court pick.