A bloodied presidential candidate Donald Trump was rushed from the stage at a Republican campaign rally in Pennsylvania after shots were fired.

Trump appeared to have been injured, with video footage showed him grimacing and raising his hand to his right ear as shots rang out from the crowd. He was seen with blood on his face.

The shooting is being investigated as an attempted assassination of the former the president and presumptive Republican nominee, law enforcement officials told The Associated Press.

The shooter was not an attendee at the rally and was killed by US Secret Service agents, the official said.

At least one attendee at the rally is believed to have been killed.

Multiple shots were heard at the outdoor rally in Butler, Pennsylvania, shortly after Trump began his speech.

Body guards then crowded around the former president as he ducked below the podium and armed officers took up positions at the front of the stage. 

Trump repeatedly raised his fist to the crowd and shouted as he was escorted to a vehicle by the US Secret Service.

The venue was abandoned with chairs knocked over and yellow police tape around the stage. A helicopter flew above and law enforcement officers walked through the area, the video feed showed. Armed law enforcement officers were also seen on a roof near the stage where Trump was standing.

Trump has since has posted on his Truth Social platform that the bullet pierced the upper part of his right ear, and there was so much bleeding, he realised what was happening’.

“I want to thank The United States Secret Service, and all of Law Enforcement, for their rapid response on the shooting that just took place in Butler, Pennsylvania,” he said..

“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. It is incredible that such an act can take place in our Country”.

Trump said nothing was known about the shooter.

“I 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. Much bleeding took place, so I realized then what was happening,” he posted.

Addressing the nation about two hours after the shooting, US President Joe Biden said “everybody must condemn” the suspected assassination attempt on Trump, adding he hoped to speak with his 2024 presidential rival soon.

Biden said he was grateful that Trump is reportedly ‘doing well’, and promised to update the public.

“We cannot allow this to be happening,” Biden said.

The Biden campaign said it was pausing all messaging to supporters and working to pull down all of its television ads as quickly as possible.

Trump and Biden are locked in a close election rematch, with most opinion polls including Reuters/Ipsos showing the two evenly matched.

Trump, who served as president from 2017 to 2021, easily bested his rivals for the Republican nomination early in the campaign and has largely unified around him the party that had briefly wavered in support after his supporters attacked the US Capitol on January 6, 2021, attempting to overturn his 2020 election defeat. 

-with AAP