Kamala Harris has broken her silence after being endorsed by Joe Biden as his successor for the Democratic presidential nomination, vowing to defeat Donald Trump.

The Vice-President wrote on X: "On behalf of the American people, I thank Joe Biden for his extraordinary leadership as President of the United States and for his decades of service to our country.

"I am honored to have the President’s endorsement and my intention is to earn and win this nomination.

"I will do everything in my power to unite the Democratic Party - and unite our nation - to defeat Donald Trump and his extreme Project 2025 agenda. If you’re with me, add a donation right now."

Joe Biden dropped out of the presidential race on Sunday following public scrutiny about his mental and physical health.

Just minutes after his announcement, Biden said he was endorsing Harris as the Democrat nominee, writing: "Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year."

In response, Donald Trump, 78, told CNN he believes she will be easier to beat.

Democrats have come out and also backed Harris at the next President of the United States.

On X, Joe Biden wrote: "My fellow Democrats, I have decided not to accept the nomination and to focus all my energies on my duties as President for the remainder of my term.

"My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it’s been the best decision I’ve made.

"Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year.

"Democrats — it’s time to come together and beat Trump. Let’s do this."