Conor McGregor sends message to Donald Trump and is thanked ...

Former president Donald Trump pumps his fist as he is helped off the stage by US Secret Service agents after the assassination attempt (Gene J Puskar/AP)

Mr Trump was addressing a campaign rally in Butler, Pennsylvania, on Saturday and was showing a chart of border crossing numbers when bangs started ringing out after 6.10pm local time.

The ex-president could be seen grimacing and reaching with his right hand towards the side of head, before blood appeared on his face.

He quickly ducked as Secret Service agents rushed the stage to surround him.

There were screams from audience members as the bangs continued, before the crowd cheered as he got back up and pumped his fist before he was taken to his motorcade.

Police evacuated the site shortly after Mr Trump left the stage.

One rally attendee was killed and two other spectators were critically injured, authorities said. All were identified as men.

The suspected gunman, who attacked from an “elevated position” outside the rally venue, was fatally shot.

There has been universal condemnation of the attack on Trump from his supporters and allies, with McGregor joining the chorus praising is battle to regain power in America,

“A 78-year-old multiple billionaire he should be on a yacht on the med touring golf courses. But he is not. He is in Pennsylvania spitting out bullets! Running for the love of his country! God speed Donald! God bless the United States,” McGregor wrote on X.

The message got a quick response from Trump’s son Don Jnr, as he replied: “Thank you for this Connor (sic). I hope more people understand exactly what is that stake these days? Never ever give up! FIGHT!!!!!”