US President Donald Trump and former vice president Joe Biden, both septuagenarians, once again publicly voiced their intense animosity toward each another, complete with threats of physical assault.

"Crazy Joe Biden is trying to act like a tough guy. Actually, he is weak, both mentally and physically, and yet he threatens me, for the second time, with physical assault," Mr Trump tweeted in the early morning.

"He doesn't know me, but he would go down fast and hard, crying all the way. Don't threaten people Joe!"

Speaking at an anti-sexual assault rally at the University of Miami yesterday, Mr Biden, who is weighing a 2020 run against Mr Trump, said he would have "beat the hell" out of the president if they had been in high school together because of his disrespect for women.

"A guy who ended up becoming our national leader said, 'I can grab a woman anywhere and she likes it,'" Mr Biden said, referencing a tape that emerged in the waning days of the 2016 campaign that showed Mr Trump boasting of his ability to grab women's genitals.

"They asked me would I like to debate this gentleman, and I said no. I said, 'If we were in high school, I'd take him behind the gym and beat the hell out of him,'" Mr Biden said.

"I've been in a lot of locker rooms my whole life. I'm a pretty damn good athlete.

"Any guy who talked that way was usually the fattest, ugliest S.O.B. in the room."

Mr Biden, who served as Barack Obama's vice president from 2009 to 2017, made similar comments during the campaign.

Mr Trump has already launched his 2020 re-election campaign.

Mr Biden is 75-years-old and Trump is 71.