Donald Trump has been spotted playing golf the day after surviving an assassination attempt, and has vowed to continue his presidential campaign with an appearance in Milwaukee on Monday (AEST).

Trump said “God alone” had prevented the “unthinkable” happening when a gunman on a roof fired shots at a Republican rally in Pennsylvania, hitting the former president on the ear.

The shooter has been identified 20-year-old Thomas Matthew Crooks, from Pennsylvania. He was registered as a Republican, according to the state’s voter records.

Crooks was shot dead by Secret Service agents seconds after he opened fire from the roof of a building about 140 metres from the stage where Trump was speaking.

An AR-15-style semiautomatic rifle was recovered near Crooks’ body.

Media report that authorities found explosives in his car, which was parked near the Trump rally in Butler.

Those who knew the shooter described him as a “loner” who was bullied at school and wore hunting clothing to class.

Crooks, who lived about an hour from the rally, reportedly graduated from Bethel Park High School in 2022.

A former classmate told the New York Post his politics was not known but “I would have pegged him as a Republican”.

When Crooks was 17 he made a $US15 ($22) donation to ActBlue, a political action committee that raises money for left-leaning and Democratic politicians, according to a 2021 US Federal Election Commission filing.

Thomas Crooks graduated from high school in 2022. Photo: Supplied

Special agent in charge of the FBI’s Pittsburgh field office Kevin Rojek said authorities had not yet identified a motive.

The rally attendee who died was named as Corey Comperatore, a fighter, who died a hero by diving on his family to protect them.

Two other people were critically injured in the incident, the FBI said.

Trump said he would remain “resilient” and not allow “evil” to win.

“Thank you to everyone for your thoughts and prayers yesterday, as it was God alone who prevented the unthinkable from happening,” he wrote on his Truth Social platform.

“We will fear not, but instead remain resilient in our faith and defiant in the face of wickedness.

Donald Trump was hit on the right ear while on stage. Photo: Getty

“Our love goes out to the other victims and their families. We pray for the recovery of those who were wounded, and hold in our hearts the memory of the citizen who was so horribly killed.

“In this moment, it is more important than ever that we stand united, and show our true character as Americans, remaining strong and determined, and not allowing evil to win.”

Trump’s wife Melania also took to social media to denounce the “monster” responsible for the “heinous act”.

“When I watched that violent bullet strike my husband, Donald, I realised my life, and Barron’s life, were on the brink of devastating change,” she said.

“A monster who recognised my husband as an inhuman political machine attempted to ring out Donald’s passion – his laughter, ingenuity, love of music and inspiration.”

Separately, Trump’s daughter Ivanka said she believed her mother Ivana, who died two years ago at the weekend, “was watching over dad last night during the attempt on his life”.

How the shooting unfolded

Trump, 78, had just started his speech when the gunfire began.

Six minutes into his speech, his head turned to the right, under a clear sky and in broiling heat.

Suddenly there was a volley of “pops” — what sounded like gunshots.

Trump immediately clutched his right ear, looked at the blood on his hand and then quickly dropped to the ground behind the podium.

The crowd screamed and those in the bleachers behind him crouched.

A half dozen Secret Service agents ran onto the stage and piled on and around Trump, who was kneeling behind the podium. Other law enforcement officers armed with rifles also took to the stage.

There was a second volley of apparent gunshots.

The shooter’s body on a roof after he was shot by the Secret Service. Photo: X

The Secret Service agents kept Trump on the ground for 25 seconds. Someone could be heard shouting: “Shooter is down!”

Someone else yelled: “Move!” as many in the crowd continued to scream.

The agents raised Trump to his feet, his red “Make America Great Again” baseball cap no longer on his head, his hair disheveled, his ear bloodied and streaks of blood smeared on his face.

“Let me get my shoes. Let me get my shoes”, Trump said, as the agents lifted him from the ground. He then said: “Wait, wait, wait”, before he started pumping his fist.

One agent raised his arm above Trump’s head, to shield it from more potential shots.

Trump continued to pump his fist towards the crowd, mouthing “fight.” Many in the crowd began chanting “USA, USA”.

As the Secret Service agents surrounded Trump and moved him to a nearby black SUV, Trump repeatedly raised his fist as they pushed him into the vehicle, to more chants of “USA”.

An eyewitness told the BBC he saw the shooter climb on the roof of a low-rise building just outside the security perimeter with a rifle and shouted to nearby police officers to alert them to the potential threat.

Police initially seemed confused and did not immediately respond to the warning, he said.

“Next thing you know, five shots rung out,” he said.

“Secret Service blew his head off. They crawled up on the roof, they had their guns pointed at him, made sure he was dead, he was dead, and that was it, it was over.”

Biden to call for unity

US President Joe Biden is expected to speak again on Monday after receiving a security briefing.

In earlier remarks at the White House, Biden condemned the assassination attempt and said he was grateful Trump was recovering from his wounds in the incident.

Biden said he would speak to Americans about the need for unity.

He said he had ordered a review of what happened at the Trump rally in Pennsylvania.

Biden directed the investigation into the Trump attack to be “thorough and swift,” and asked people not to “make assumptions” about the gunman’s motive.

“There is no place in America for this kind of violence or any violence for that matter. An assassination attempt is contrary to everything we stand for … as a nation — everything,” he said.

Biden’s planned remarks came after homeland security and law enforcement officials briefed him, and as the White House continued to call for national unity and condemn the act of violence.

Trump is pushing ahead with plans to attend this week’s Republican National Convention in Milwaukee.

-with AAP