American law enforcement agencies have identified the man who attempted to assassinate former US president Donald Trump at a rally in Pennsylvania as 20-year-old Thomas Matthew Crooks of Bethel Park.

He was shot dead by Secret Service officials after the attack.

The gunman was immediately “neutralized” by the Secret Service, chief of communications Anthony Guglielmi told NBC News.

Pennsylvania voter records listed a Thomas Matthew Crooks with the same address and birth date as a registered Republican, though it was not clear from the records when that was put in place, the news channel reported.

Former US President Donald Trump received injuries on his right ear during a Saturday election campaign rally at Pennsylvania's Butler, in what is seen as an assassination bid that left the 78-year-old Republic.

can presidential candidate's face streaked with blood with his alert security agents rushing him off the stage even as he pumped his fist in the air, mouthing the words "Fight! Fight! Fight!"

As gunshots were heard, Trump, who was just six minutes into his election speech, was seen clutching a hand to his right ear, where blood was visible across his cheek and mouth.

Two other spectators were injured, the Secret Service said in a statement. The incident was being investigated as an assassination attempt.

Secret Service agents were quick to respond and surrounded Trump while escorting him off the stage, as he raised a fist to the crowd in defiance.