The FBI has identified 20-year-old Thomas Matthew Crooks as the gunman who fired shots at former President Donald Trump during a campaign rally in Butler, Pennsylvania.

"The FBI has identified Thomas Matthew Crooks, 20, of Bethel Park, Pennsylvania, as the subject involved in the assassination attempt of former President Donald Trump on July 13, in Butler, Pennsylvania," the Bureau said in a statement.

"This remains an active and ongoing investigation, and anyone with information that may assist with the investigation is encouraged to submit photos or videos online at FBI.gov/butler or call 1-800-CALL-FBI."

Crooks was killed by a Secret Service sniper at the rally, officials said.

"We do not currently have an identified motive," said Kevin Rojek, FBI Pittsburgh special agent in charge, at a briefing Saturday night.

Federal investigators said the gunman was not carrying identification, so they analyzed his DNA to provide a biometric confirmation of his identity.

Trump was shot at during a rally in Pennsylvania. He was quickly bundled off stage and into a waiting vehicle and has since returned home to New Jersey.

In a post to his Truth Social network, Trump said a bullet pierced the "upper part" of his right ear.

Earlier, his spokesperson said he was receiving treatment at a local medical centre.

"I knew immediately that something was wrong in that I heard a whizzing sound, shots, and immediately felt the bullet ripping through the skin," Trump wrote. "Much bleeding took place, so I realized then what was happening."

Blood was clearly visible on Trump's ear and face as protection officers rushed him away.

The suspect was shot dead at the scene by US Secret Service officers, the agency's spokesperson Anthony Guglielmi said.

He added that one bystander was killed in the shooting and two others were critically injured. All three victims were male.

Prestar:
Imagine 20-years-old
Something that can't happen in Nigeria