(Reuters) - Elon Musk, the billionaire CEO of Tesla, said he "fully endorsed" Donald Trump, calling the Republican presidential candidate "tough."

Trump was safe, the U.S. Secret Service and his campaign said on Saturday after multiple shots rang out at his rally in Pennsylvania as video showed Trump grimacing and raising a hand to his right ear.

"I fully endorse President Trump and hope for his rapid recovery," Musk posted on his social media platform X.

Earlier, multiple shots rang out at Donald Trump's rally in Pennsylvania on Saturday, with the Republican presidential candidate grimacing and raising his right hand to his right ear as shots rang out, video footage showed.

Musk later posted a photograph of Trump at the event, followed by: "Last time America had a candidate this tough was Theodore Roosevelt."

Representatives from social media company X, which Musk runs, did not immediately respond to a request for comment.

Musk, who has been ramping up criticism of U.S. President Joe Biden, has donated to a political group working to elect rival presidential candidate Donald Trump, Bloomberg reported on Friday, citing sources.

In March, Trump, a former U.S. president who is expected to be formally nominated next week as the Republican Party's candidate for the Nov. 5 election, met with Musk and other wealthy donors.

In response to reports of the meeting, South Africa-born Musk posted on X: "Just to be super clear, I am not donating money to either candidate for US President." In May, he also denied media reports that there had been talks over a potential advisory role for him in any Trump presidency.