US President Joe Biden has dropped out of the presidential race. He has endorsed Vice President Kamala Harris to be the Democratic Party's nominee to take on Republican Donald Trump in November.

Biden made the announcements on his X account on Sunday. He says it is "in the best interest" of his party and the country for him to stand down to focus solely on fulfilling his duties as president for the remainder of his term.

The president added that he will speak to the nation later this week in more detail about his decision.

Calls had been growing among Democrats for Biden to quit his campaign after his faltering performance in last month's debate against Trump.

Biden had already acquired more than 90 percent of state delegates in the contest to choose the Democratic candidate.

He was set to become the party's official candidate by giving a nomination acceptance speech at the party's national convention in mid-August.

It is believed that Biden's exit will allow about 4,000 state delegates to vote for a candidate at their own discretion.

This is the first time in 56 years that an incumbent president seeking reelection has dropped out of an election campaign. The last president that did so was Lyndon Johnson in 1968.

Democratic National Committee Chair Jaime Harrison says the party will undertake a transparent and orderly process to move forward in the coming days.