The former president has posted on his Truth Social platform that the bullet pierced the upper part of his right ear, and there was so much bleeding, he realised what was happening'.

"I want to thank The United States Secret Service, and all of Law Enforcement, for their rapid response on the shooting that just took place in Butler, Pennsylvania," Trump said.

"Most importantly, I want to extend my condolences to the family of the person at the Rally who was killed, and also to the family of another person that was badly injured.

"It is incredible that such an act can take place in our Country. Nothing is known at this time about the shooter, who is now dead.

"I was shot with a bullet that pierced the upper part of my right ear. I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin.

"Much bleeding took place, so I realized then what was happening."

Trump was spattered with blood when gunfire erupted at his rally in Butler on Saturday, sparking panic in the crowd, with one attendee reported to have been killed, and another critically injured.

The Republican candidate pumped his fist in the air as he was surrounded by security, and appearing to mouth the words "Fight! Fight! Fight!"

The alleged shooter is dead and the Secret Service was investigating the shooting as an assassination attempt, sources say.

As the shots rang out, Trump grabbed his right ear with his right hand, then dropped to his knees behind the podium before Secret Service agents swarmed and covered him.

The Secret Service and the former president's campaign said Trump was safe following the shooting.

The shooter's identity and motive were not immediately clear.

With AAP.