The US Secret Service said former president Donald Trump was "safe" after he was rushed off stage when gunshots were fired at a campaign rally on Saturday in Pennsylvania.

As the bangs rang out, 78-year-old Trump grimaced and clutched a hand to his right ear, with blood soon visible across his face.

Secret Service agents swarmed onto the podium, surrounded the Republican candidate and escorted him roughly off the stage, as Trump raised a fist to the crowd.

The suspected shooter was confirmed dead, along with one bystander, US media reported.

"The former president is safe," the Secret Service said in a post on X, and his campaign said he was "fine" and being checked at a medical facility.

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

President Joe Biden, who is set to face Trump in a bitter replay of their 2020 clash, said there was "no place for this kind of violence in America".

"I'm grateful to hear that he's safe and doing well," Biden said in a statement, adding: "I'm praying for him and his family and for all those who were at the rally."

The 81-year-old, staying at his house in Rehoboth, Delaware, gave a televised statement repeating his message, saying "we cannot be like this".

The shooting took place shortly after Trump took the stage at his final campaign rally before the Republican National Convention in Milwaukee next week. (AFP)