Kanye West, the entertainment mogul who urges listeners in one song to "reach for the stars, so if you fall, you land on a cloud," announced on Saturday he is challenging Donald Trump for the US presidency in 2020.

"We must now realise the promise of America by trusting God, unifying our vision and building our future. I am running for president of the United States! #2020VISION," the born-again billionaire rapper tweeted as Americans marked Independence Day.

He offered no further details on his campaign, four months before the November election. The 43-year-old gained the endorsement of Elon Musk, the CEO of SpaceX who responded the tweet. He wrote: "You have my full support."