American rapper Kanye West, a vocal supporter of US President Donald Trump, announced on Saturday that he would run for president in 2020 in an apparent challenge to Trump and his presumptive Democratic rival, former Vice President Joe Biden.

"We must now realize the promise of America by trusting God, unifying our vision and building our future. I am running for president of the United States," West wrote in a Twitter post, adding an American flag emoji and the hashtag "#2020VISION".

It was not immediately clear if West was serious about vying for the presidency four months before the Nov. 3 election or if he had filed any official paperwork to appear on state election ballots.