Former United States President Donald Trump was on stage at a rally in Pennsylvania's Butler before gunshots rang out and Secret Service agents stormed the stage.
Trump, 78, was hit by a bullet in the upper part of his right ear when the suspected shooter fired multiple shots toward the stage from an elevated position outside of the rally venue, the US Secret Service said.
The Secret Service agents surrounded the Republican candidate and escorted him off the stage, with blood visible across his face, The Hill reported.
Trump raised his fist towards the crowd as he was escorted away by law enforcement personnel.
According to the US Secret Service's statement, one spectator was killed and another was critically injured and the incident is being investigated.
The US Secret Service personnel neutralised the shooter.
How American leaders reacted to attack on Trump
Bullet pierced upper part of my ear: Trump
Modi, Rahul condemn attack on Donald Trump
Donald J Trump Makes History!