BUTLER, United States - A witness to Saturday's shooting at a Donald Trump rally told how a man next to him was shot dead during the apparent assassination attempt on the Republican presidential candidate.

"I heard several gunshots. The man beside me suffered a gun shot to the head, was instantly killed (and) fell to the bottom of the bleachers. Another woman looked like she got hit in the forearm or hand," the man, whose name was only given as Joseph, told NBC News.

He said it seemed the victim was "in the way of the shots between whoever was shooting the gun and the president."

Trump said he was hit in the ear but was not seriously injured by the gunman, who was killed after the incident. Two other spectators were critically injured, the Secret Service said.

AFP