Donald Trump has insisted that Joe Biden would "go down fast and hard, crying all the way" after the Democrat threatened to "beat the hell out of" the US president if they were at school.

Mr Biden, the former US vice-president, said earlier this week that he would have taken Mr Trump "behind the gym" and beaten him up over his crude comments about women.

The 75-year-old spoke at an anti-sexual assault rally in Florida on Tuesday and cited lewd comments Mr Trump made in a 2005 "Access Hollywood" tape about grabbing women.

Mr Biden reportedly said: "If we were in high school, I'd take him behind the gym and beat the hell out of him."

But Mr Trump lashed out at Mr Biden in a tweet on Thursday, saying he "would go down fast and hard, crying all the way."

Saying "Don't threaten people Joe!", he said Mr Biden is "trying to act like a tough guy", but "actually, he is weak, both mentally and physically, and yet he threatens me, for the second time, with physical assault".