US President Joe Biden has ended his re-election campaign and endorsed Vice-President Kamala Harris to succeed him as the Democratic candidate, in an extraordinary decision that upends an already dramatic race for the White House.

Mr Biden, 81, said in a Sunday written statement that it was the “greatest honour” to serve but his withdrawal was “in the best interest of my party and the country”.

The announcement caps a tumultuous period in US politics, which began with his sometimes incoherent debate performance against Donald Trump on 27 June. Mr Biden says he will remain president until January.

Ms Harris, 59, said that she was “honoured” to be endorsed, adding she would “earn and win this nomination” and unite the country against Trump.

“We have 107 days until election day,” she said. “Together, we will fight. And together, we will win.”