Former US president Donald Trump survived an apparent assassination attempt when he was grazed by a bullet shortly after the start of his rally in Butler, Pennsylvania, on Saturday evening.

The suspected sniper and a person attending the rally were killed. Two other spectators were reportedly critically injured. The incident was being investigated as an assassination attempt, a source told Reuters.

Around 6:15 pm EDT, Trump reflexively reached for his right ear after several popping sounds as Secret Service agents yelled "Get down! Get down!", according to a widely circulated video, which was taken close to the front of the stage.

Trump, 78, ducked about two seconds later and was swarmed by security.

Agents piled atop Trump to shield him with their bodies as other agents took up positions on stage to search for the threat.

Trump then eventually stood up and defiantly pumped his fist, bleeding from the top of his right ear. Blood streaks also could be seen across the right side of his face.

Trump could be heard yelling "Fight! Fight! Fight" to the crowd in the immediate aftermath and said, "Let me get my shoes."

He was rushed into his limousine by more than a dozen agents shortly afterward and taken to a medical facility.

Trump issued a statement on Truth Social late Saturday, thanking law enforcement and offering sympathy for the person killed at the rally and the one who was injured.

He added: "I was shot with a bullet that pierced the upper part of my right ear. I knew immediately that something was wrong and that I heard a whizzing sound of shots, and immediately felt the bullet ripping through the skin. Much bleeding took place, so I realized then what was happening."

The attack apparently came from a sniper positioned on a building hundreds of yards from the former president — outside the security cordon, according to law enforcement sources, the New York Post reported.

The shooter was engaged by members of the Secret Service counterassault team and killed, according to two officials who spoke on the condition of anonymity to discuss the ongoing investigation publication, The Associated Press reported.

"Shooter is down," could be heard on the video.

The heavily armed tactical team travels everywhere with the president and major party nominees and is meant to confront any active threats while other agents focus on safeguarding and evacuating the protectee.

"President Trump thanks law enforcement and first responders for their quick action during this heinous act," said Trump spokesman Steven Cheung in a statement. "He is fine and is being checked out at a local medical facility. More details will follow."

The Associated Press, in a bulletin at 7:24 pm EDT, reported "JUST IN: Shooter dead and rally attendee killed at Trump event in Pennsylvania, Butler County district attorney tells AP."

"Quite frankly I don't know how he (the shooter) would have gotten to the location where he was, but he was outside the grounds and I think that's something that we're going to have to figure out — how he got there," District Attorney Richard Goldinger told CNN.

A man who said he and his friends were attending a party outside the rally told the BBC in a video on X they had noticed "a guy … bear crawling up the roof of the building beside us. … We're pointing at the guy crawling up the roof. … You can clearly see him with a rifle. … We're like, "Hey, man. There's a guy on the roof with a rifle," he said they told police.

"Hey right here on the roof, we can see him from right here … he's crawling. … I'm thinking why is Trump still speaking. Why have they not pulled him off the stage? I'm standing there pointing at him (the sniper) for two or three minutes, and the Secret Service is looking at us from the top of the barn. … Next thing you know, five shots rang out. … Secret Service blew his head off."

The city of Butler is located about 35 miles north of Pittsburgh. Pennsylvania is considered a crucial state for the presidential election in November.

The incident occurred two days before the start of the Republican National Convention in Milwaukee, where Trump will be nominated as the GOP presidential candidate.

Donald Trump Jr. issued a statement saying, "I just spoke to my father on the phone and he is in great spirits. He will never stop fighting to save America, no matter what the radical left throws at him."

"Look, there's no place in America for this kind of violence," President Joe Biden said in a nationally televised statement from Delaware. "It's sick. It's sick. It's one of the reasons why we have to unite this country. We cannot allow for this to be happening."

Biden said he had hoped to speak to "Donald" on Saturday night.

Former president Barack Obama said in a statement: "There is absolutely no place for political violence in our democracy. Although we don't yet know exactly what happened, we should all be relieved that former President Trump wasn't seriously hurt, and use this moment to recommit ourselves to civility and respect in our politics. Michelle and I are wishing him a quick recovery."

In a statement, former president George W. Bush said: "Laura and I are grateful that President Trump is safe following the cowardly attack on his life. And we commend the men and women of the Secret Service for their speedy response."

Pennsylvania Governor Josh Shapiro, a Democrat, said in a statement on X that he had been briefed on the situation and Pennsylvania state police were on hand at the rally site.

"Violence targeted at any political party or political leader is absolutely unacceptable. It has no place in Pennsylvania or the United States," he said.

Now an already intense US presidential election campaign appears to be greatly affected again, with the focus likely to shift to security for candidates.

Ian Bremmer, president and founder of GZERO Media, noted that the incident is a "very grave" turn of events in a country that is very deeply polarized.

"This is the worst sort of event that can happen in that environment, and I deeply worry that it presages much more political violence and social instability to come," Bremmer, also President and Founder of GZERO Media's parent company, Eurasia Group,said in a video comment.

Most of the campaign news lately has been centered on whether Biden, 81, will keep the Democratic nomination following his halting performance in a debate with Trump on June 27 and notable verbal flubs in a subsequent interview and press conference that have led for calls by numerous Democratic politicians and partisan celebrities for him to step aside.

Trump is facing sentencing in New York after a campaign fraud trial. The sentencing, which was pushed back to September from July following a recent Supreme Court ruling on presidential immunity, could be affected by the court's decision.

House Speaker Mike Johnson, a Louisiana Republican, said Saturday, "The American people deserve to know the truth" about the shooting.

"We will have Secret Service Director Kimberly Cheatle and other appropriate officials from DHS and the FBI appear for a hearing before our committees ASAP," Johnson said.

The White House said Biden spoke with Trump on Saturday evening. The president, who will return to the White House from Delaware earlier than planned, will convene a briefing with homeland security and law enforcement officials at the White House on Sunday morning, the AP reported.

Agencies contributed to this story.