US President Joe Biden has announced that he will end his candidacy for re-election, upending the race for the White House four months before Americans go to the polls in November.

The decision comes after weeks of intense pressure from fellow Democrats following a stumbling and sometimes incoherent debate performance against Republican Donald Trump at the end of June.

The 81-year-old had resisted calls to step aside even as concerns over his mental fitness and capacity to beat Trump mounted.

The announcement paves the way for another Democrat to become the party’s presidential candidate, with Vice-President Kamala Harris the most likely successor.

He will remain president until January, when the winner of the 2024 election will take office.