Chicago | Former US president Donald Trump was injured after being shot in the ear during an apparent assassination attempt at an election rally in Pennsylvania after which a male attacker was shot and killed by a member of the Secret Service.

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 in Butler on Saturday, the US Secret Service said.

The attacker killed one spectator at the rally, and two others were critically injured.

Secret Service agents swarmed Trump and ducked behind the podium. Blood could be seen on his right ear of Trump as agents surrounded him and led him off the stage to a waiting vehicle to whisk him away.

Trump said, “Let me get my shoes,” as he was escorted to the safe place. He was seen pumping his fist to the shocked supporters.

The shooting is being investigated as an attempted assassination, law enforcement officials said.

“US Secret Service personnel neutralised the shooter, who is now deceased. The US Secret Service quickly responded with protective measures and Former President Trump is safe,” Anthony Guglielmi, Secret Service spokesperson said in a statement.

"This incident is currently under investigation. and the Secret Service has notified the FBI,” he said.

The suspect fired from between 200ft and 300ft away on an elevated shed with an AR-style rifle, multiple law enforcement officers told CBS News.

Trump is "fine," a spokesperson said.

“As was communicated earlier this evening, President Trump is doing well and grateful to law enforcement and first responders for their fast action,” his campaign said.

The incident happened two days before the start of the Republican National Convention in Milwaukee, where Trump will formally become the party’s nominee for the November 5 presidential election.

“President Trump looks forward to joining you all in Milwaukee as we proceed with our convention to nominate him to serve as the 47th President of the United States. As our party's nominee, President Trump will continue to share his vision to Make America Great Again,” his campaign said.

Trump said he 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." the former president posted on his Truth Social account.

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

US President Joe Biden spoke to Trump, his November election opponent, a White House official said.

The White House official did not say what the two spoke about.

Biden also talked with Pennsylvania Governor Josh Shapiro and Butler Mayor Bob Dandoy, the White House said.

Biden was scheduled to be in Delaware for the weekend but changed his plans to return to the White House.

Biden earlier said that “everybody must condemn” the suspected assassination attempt.

Addressing the nation about two hours after the shooting, he said “We cannot allow this to be happening,” Biden said. “The idea that there's violence in America like this is just unheard of."

Thousands of Trump supporters were attending the rally when the shooting, which was captured live on news channels, happened. The shooting created chaos with people in the back of the venue immediately running to the exits.

Vice President Kamala Harris and former presidents, Barack Obama, George W Bush and Bill Clinton have condemned the attack on Trump.

Harris says she is "relieved" Trump was not seriously injured.

"We are praying for him, his family, and all those who have been injured and impacted by this senseless shooting," Harris said in a statement.

"Violence such as this has no place in our nation. We must all condemn this abhorrent act and do our part to ensure that it does not lead to more violence," she said.

Trump's daughter, Ivanka Trump, also issued a statement.

"Thank you for your love and prayers for my father and for the other victims of today's senseless violence in Butler, Pennsylvania," she said in a statement on X.

"I am grateful to the Secret Service and all the other law enforcement officers for their quick and decisive actions today. I continue to pray for our country. I love you Dad, today and always."

Trump also thanked the Secret Service and other law enforcement "for their rapid response to the shooting that just took place".

"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," he said in the post.

"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," he added.

He ended the post with, "GOD BLESS AMERICA!"