A man who watched the horrific assassination attempt on Donald Trump revealed he warned Secret Service agents about a gunman on a nearby roof minutes before shots rang out. 

The stunned witness, named only as Greg, told the BBC he saw the would-be assassin climb onto the top of a building outside the event in Butler, Pennsylvania, and that he was bewildered by the lack of action from agents.

He said: 'I’m thinking to myself, why is Trump still speaking, why have they not pulled him off the stage? The next thing you know, five shots ring out.'

After the gunman opened fire he saw the Secret Service 'blow his head off,' the man said.

Agents then climbed onto the roof, where the gunman was and images from social media appeared to show a man lying lifeless. 

The witness, a Trump supporter, told the BBC how he had seen the shooter prepare to assassinate the former president.

Other rally attendees also saw him on the roof for three or four minutes with no action taken by law enforcement, he said. 

He said: 'We noticed a guy crawling, you know army, bear crawling up the roof of the building 50ft away from us.

'So we are standing there pointing at the guy crawling up the roof, he had a rifle, we could clearly see he had a rifle.

'We are pointing at him, the police are down there running around on the ground. We are like hey man there is guy on the roof with a rifle - and the police are like "hey what? you know", they didn't know what was going on.

'We are like we can see him right here on the roof he's crawling. The next thing you know, I am like why is Trump still speaking? Why have they not pulled him off the stage? 

'I'm standing there pointing at him for two-three minutes, the secret service is looking at us from the top of the barn - I'm pointing at that roof.'

When asked if he was certain if the shots came from the man on the roof, the Trump supporter replied: '100 per cent, 100 per cent.'

Moments later Secret Service agents could be heard shouting 'the shooter is down'.

The agency confirmed the incident is being investigated as an attempted assassination. 

The witness said the Secret Service 'probably' could not see the shooter the shape of the roof would have blocked their line of sight. 

'But why is there not Secret Service on all of these roofs here?' the man asked.

'I mean this is not a big place.'

At least eight bullets were fired moments after Trump got up to speak, and the president was seen grabbing the side of his head as blood poured from his ear and screams from terrified onlookers rang out. His team says that he is 'fine.'

It has since been reported that Trump may have been struck by a piece of flying glass from a teleprompter shattered during the shooting.

The identities of the shooter and the dead bystander have not yet been confirmed. It is also unclear where the shooter opened fire from and what kind of weapon was used.

In an image that has already gone around the world, Trump was pictured repeatedly pumping his fist with blood dripping from his face while being surrounded by Secret Service agents.

Moments later, he was rushed away to safety. Trump's team said further updates on the former president's condition will follow soon.

His son Donald Trump Jr has since shared a post of his bloodied father with his fist clenched on X, captioned: 'He'll never stop fighting to save America.'

A spokesman added that the GOP 2024 hopeful added that Trump 'thanks law enforcement and first responders for their quick action during this heinous act.'

The DA added that an attendee was also killed at the rally, which was being held in Butler, Pennsylvania, on Saturday afternoon.

Within seconds, Trump was put to the floor by several Secret Service agents to protect him from the shooter, as the press pool said 'residual bangs' were heard after Trump hit the floor.

Trump stood up shortly after and pumped his fist at the crowd, leading to chants of 'USA' and 'Make America Great Again.'

He appeared to mouth the word 'fight' to supporters at the same moment.

Moments before he appeared to be hit, Trump was using a graphic at the rally to speak about illegal immigration.

Secret service encircled Trump within seconds of the shots being fired, and the agency said in a statement that the former president is 'safe.'

'The Secret Service has implemented protective measures and the former President is safe. This is now an active Secret Service investigation and further information will be released when available,' the statement read.

The extent of Trump's injuries are not clear, although he appeared to want to show his supporters that he was okay moments after being shot.

President Biden said in a statement that American 'must unite as one nation' in response to the horrific scenes.

'I have been briefed on the shooting at Donald Trump’s rally in Pennsylvania. I’m grateful to hear that he’s safe and doing well,' the White House said in a statement.

'I’m praying for him and his family and for all those who were at the rally, as we await further information.'

In a press conference later in the evening, Biden described the incident as 'sick', and said there is 'no place in America for this kind of violence.'

A spokesperson for the ATF said agents from the bureau have been deployed to assist with the aftermath of the chaos.

Rep. Dan Meuser, R-Pa., was standing front row at the rally along with Reps. Mike Kelly and GOP Senate candidate Dave McCormick.

Meuser said he heard between eight to 10 shots ring out as screams rippled through the crowd, according to Fox News.

He added that it appeared there were multiple people in the crowd may have been impacted by the bullets and the local district attorney confirmed that at least one person is 'believed to be dead.'

Pennsylvania Governor Josh Shapiro condemned the shocking scenes in his state.

'Violence targeted at any political party or political leader is absolutely unacceptable,' Shapiro said on X.

'It has no place in Pennsylvania or the United States. I have been briefed on the situation. @PAStatePolice are on the scene in Butler County and working with our federal and local partners.'

An emergency room doctor at the Trump rally revealed how he performed CPR on a member of the crowd after the attempted assassination.

'I heard the shots. I thought it was firecrackers begin with. Somebody over there was screaming 'he's been shot he's been shot,'' said the man who had blood splattered all over his white USA shirt. 'So I made my way over. I said I'm an emergency department physician. Let me help you.'

'The guy had spun around was jammed between the benches and a head shot here. There's lots of blood and he had brain matter,' he told CBS News.