President Joe Biden overshadowed his vice president Kamala Harris' big 'closing' campaign speech by calling Donald Trump's supporters 'garbage' in an astonishing outburst. 

The 81-year-old commander-in-chief's bombshell gaffe evoked memories of Hillary Clinton's infamous dismissal of Trump voters as 'deplorables' in 2016, which contributed to her shock defeat.

It came as Harris was hoping to capture the nation's full attention with a carefully planned rally in front of the White House for 75,000 Democrats one week before Election Day. Harris used the event on Tuesday night to make her final case, declaring she would be a unifying president 'for all Americans'.

However, Biden, on a separate Zoom call with supporters, stepped on her moment by appearing to lash out at Trump supporters in what Republicans lambasted as a 'disgusting' attack.

The president was weighing in after a comedian at Trump's Madison Square Garden rally on Sunday compared Puerto Rico to a 'floating island of garbage'.

Biden said: 'The only garbage I see floating out there is his (Trump's) supporters.'

Trump seized on Biden's comment, declaring it was 'worse' than what Clinton said eight years ago, and Democrats immediately began distancing themselves from the president.

Biden later disputed that he had called Trump supporters 'garbage'. He said that by 'garbage' he meant 'hateful rhetoric' that had been on display at the Madison Square Garden rally.

He made the incendiary comment on a Zoom call organized by the advocacy group Voto Latino.