Secret Service agents have rushed former President Donald Trump off stage after what sounded like gunshots rang out at a rally in Pennsylvania.
Footage showed him grimace and raise a hand to his ear, before ducking as sharp cracks – apparently shots – broke out.
He was quickly swarmed by secret service agents and rushed off stage to a waiting vehicle.
In a statement Trump’s campaign said he was “fine” and was being “checked out” at a local medical facility.
“President Trump thanks law enforcement and first responders for their quick action during this heinous act,” spokesman Steven Cheung said.
The former president appeared to have blood on his right ear and raised a fist as he was bundled off stage and into a car.
Armed police took to the podium soon after.
In a statement, the Secret Service said Trump was safe and that measures for his protection had been implemented.
They added that an active investigation was now under way and that further information would be released when available.
The Republican candidate for president had been addressing his supporters in Butler, Pennsylvania – a crucial swing state in November’s election.
Multiple bangs rang out as Trump spoke about his successor, President Joe Biden, and his administration.
Several supporters holding placards and standing behind Trump ducked as the apparent shots were heard.
One witness, Jason, told the BBC that he heard five shots, which went off in quick succession.
“We see the Secret Service jump on Trump to protect him. Everyone in the crowd dropped down very quickly,” he said.
“He shortly thereafter stood up and put his fist up in the air, said a couple of things.”
Tim – who was also at the rally – told the BBC that he had heard a “barrage” of shots.
“There was a spray which we initially thought was a fire hose, and then the speaker on the right hand side started coming down,” he said.
“Something must have hit the hydraulic lines [which caused it to fall]. We saw President Trump go to the ground and everyone started dropping to the ground because it was chaos.”
The White House said President Biden, who is in his home state of Delaware, had received an initial briefing.
Politicians of both parties have condemned the apparent attack.
Pennsylvania Governor Josh Shapiro, a Democrat, said “violence targeted at any political party or political leader is absolutely unacceptable”.
Former Vice-President Mike Pence said he and his wife were praying for Trump, adding that he urged “every American to join us”.
House Minority Leader Hakeem Jeffries said in a statement: “My thoughts and prayers are with former President Trump. I am thankful for the decisive law enforcement response. America is a democracy. Political violence of any kind is never acceptable.”
