US President Donald Trump has reaffirmed his support for his Supreme Court nominee Brett Kavanaugh after a lengthy Senate committee hearing into allegations he sexually assaulted someone when he was 17 years old.

Mr Kavanaugh angrily and tearfully denied a university professor's accusation that he sexually assaulted her 36 years ago after she told a dramatic US Senate hearing she was "100% certain" he did it.

Christine Blasey Ford appeared in public for the first time to detail her allegation against Mr Kavanaugh, a conservative federal appeals court judge chosen by Mr Trump for a lifetime job on the top US court.

Dr Ford told the committee she feared Mr Kavanaugh would rape and accidentally kill her during the alleged assault when both her high school students in Maryland.

Mr Kavanaugh testified after Dr Ford finished her appearance, and they were never in the hearing room together.

The clash pitted her word against his.

"I swear today, under oath, before the Senate and the nation, before my family and God, I am innocent of this charge," Mr Kavanaugh told the Judiciary Committee.

Calling himself a victim of "grotesque and obvious character assassination," Mr Kavanaugh, speaking passionately, said he "unequivocally and categorically" denied Dr Ford's allegation.

"I will not be intimidated into withdrawing from this process," Mr Kavanaugh added.

Mr Kavanaugh at times choked back tears, especially when he mentioned that his daughter suggested they pray for Dr Ford, when he spoke of his father and when he mentioned women friends who have rallied to support him.

He also sharply attacked Democratic senators, calling himself the victim of "a calculated and orchestrated political hit" fueled by anger on the left at Trump's 2016 election win.

Mr Kavanaugh tangled with Democratic senators, at one point repeatedly interrupting Senator Patrick Leahy.

Dr Ford, a psychology professor at Palo Alto University in California, said over four hours of testimony that a drunken Mr Kavanaugh attacked her and tried to remove her clothing at a gathering of teenagers when he was 17 years old and she was 15 in 1982.

The hearing, which has riveted Americans and intensified the political polarisation in the US, occurred against the backdrop of the #MeToo movement against sexual harassment and assault.

Writing on Twitter after the hearing, Mr Trump said of Mr Kavanaugh: "His testimony was powerful, honest, and riveting. Democrats' search and destroy strategy is disgraceful and this process has been a total sham and effort to delay, obstruct, and resist. The Senate must vote!"

"With what degree of certainty do you believe Brett Kavanaugh assaulted you?" Democratic Senator Richard Durbin asked Dr Ford.

"100%," she replied, remaining firm and unruffled through hours of testimony even under questioning by a sex crimes prosecutor hired by the committee's Republicans.

Dr Ford said "absolutely not" when Democratic Senator Dianne Feinstein asked her if it could be a case of mistaken identity, as Mr Kavanaugh has suggested.

Democrats lauded Dr Ford's testimony as credible, brave and, in the words of Senator Cory Booker, "nothing short of heroic".

"I want to thank you for your courage. And I want to tell you I believe you ... And I believe many Americans across the country believe you," Democratic Senator Kamala Harris said.

While some Republicans and Mr Trump have called the allegations by Dr Ford and the two other women part of a smear campaign, she told the committee she had no political motivation, adding: "I am an independent person and I am no pawn."

Dr Ford was seated at a table in the packed hearing room flanked by her lawyers, facing a bank of senators.

She told the senators she was "terrified" to testify but felt it was her civic duty come forward.

Brett Kavanaugh has denied all allegations against him

"Brett groped me and tried to take off my clothes. He had a hard time because he was very inebriated and because I was wearing a one-piece bathing suit under my clothing. I believed he was going to rape me. I tried to yell for help," Dr Ford said, adding that Mr Kavanaugh and a friend of his, Mark Judge, were "drunkenly laughing during the attack".

Democratic senators sought to score political points during their five minutes apiece of questioning Dr Ford. The panel's Republican senators, all men, did not question her, assigning that task to Rachel Mitchell, a sex crimes prosecutor.

While Ms Mitchell sought to probe Dr Ford's account including any gaps in her story, her questioning seemed disjointed.

She took turns with the Democratic senators to ask questions in five minute segments, disrupting her flow.

The controversy has unfolded just weeks ahead of the 6 November congressional elections in which Democrats are trying to seize control of Congress from the Republicans.

Mr Kavanaugh's confirmation would cement conservative control of the high court as Mr Trump moves to shift it and the broader federal judiciary to the right.

Mr Kavanaugh, sitting alone at the witness table, said he wanted to testify as soon as Dr Ford's allegation first emerged last week and was not surprised that other allegations followed.

"In those ten long days, as was predictable and as I predicted, my family and my name have been totally and permanently destroyed by vicious and false additional accusations."

The delay in scheduling a hearing "has been horrible to me and my family, to the Supreme Court and to the country," Mr Kavanaugh said.

Looking sombre, Mr Kavanaugh was accompanied by his wife as he entered the hearing room.

He accused the Democrats of "lying in wait," with the Dr Ford allegations, only revealing them publicly after his original confirmation hearing was completed. He thanked Mr Trump for his "steadfast support."

He was careful not to denounce Dr Ford, noting that he wished her "no ill will."

He said that he was not questioning that Dr Ford may have been sexually assaulted by some person in someplace at some time, but that he had never assaulted her or anyone.

Supreme Court appointments must be confirmed by the Senate. The Republicans control the Senate by a narrow 51-49 margin. That means that a handful of moderate Republican senators who have not announced whether or not they support Mr Kavanaugh could determine his fate.

One of them, Senator Lisa Murkowski, told Reuters: "I find Dr Ford's testimony to be credible."

The committee could vote on Mr Kavanaugh's confirmation on Friday, with a final Senate vote early next week.

Prosecutor Rachel Mitchell

Some Democrats have called on Mr Kavanaugh to withdraw in light of the allegations. At the hearing, Republican Senator Lindsey Graham castigated Democratic senators, seeking to rally Republicans not to abandon the nominee.

"This is the most unethical sham since I've been in politics," Mr Graham said, adding that voting against Mr Kavanaugh would legitimise the attacks on the nominee.

Dr Ford said Mr Kavanaugh put his hand over her mouth to stop her from screaming during the assault, adding: "This was what terrified me the most, and has had the most lasting impact on my life. It was hard for me to breathe, and I thought that Brett was accidentally going to kill me."

Her strongest memory of the incident, Dr Ford said, was the "uproarious laughter between the two (Mr Kavanaugh and Mr Judge) and their having fun at my expense". She said the laughter has haunted her ever since.

A White House official described Mr Trump's reaction to Mr Kavanaugh's dramatic defence as positive, saying the nominee significantly helped his case after Dr Ford's testimony.

"People are going to walk away from this thing feeling that there are two passionate, credible people talking," the official said.

"I think every Republican has a fair reason to vote for him and not a real fair reason not to vote for him," the official added.

Two other women, Deborah Ramirez and Julie Swetnick, have accused Mr Kavanaugh of sexual misconduct in the 1980s.

Ms Ramirez accused Mr Kavanaugh of exposing himself during a drunken dormitory party during the 1983-84 academic year when both attended Yale University.

Ms Swetnick said she witnessed efforts by Mr Kavanaugh and others to get girls drunk at parties so they could be raped. She said Mr Kavanaugh was present at a 1982 party where she was raped.

Mr Trump, who has himself faced accusations of sexual misconduct, chose Mr Kavanaugh to replace Justice Anthony Kennedy, who retired in July.