Former US president Donald Trump was "safe" after he was rushed off stage when gunshots were fired at a campaign rally on Saturday in Pennsylvania, in a shocking incident that will fuel anxiety in the run-up to the 2024 election.

As the bangs ran 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 in defiance.

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.

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 ramps up tension in a country already on edge about the prospect of unrest and political harassment before the November election.

It took place shortly after Trump took the stage at his final campaign rally before the Republican National Convention in Milwaukee next week.

"Butler County District Attorney Richard Goldinger said two people are dead, including an apparent shooter," The Washington Post reported. A second bystander may also have been hit.

The rally in Butler, Pennsylvania descended into chaos after shots were heard and screams and shouts rang out.

"Let me get my shoes," Trump was heard saying on microphone, as security agents helped him back to his feet.

He turned back to the crowd and repeatedly raised his fist, as well as mouthing words that weren't immediately discernable, in what is set to become an iconic image.

Agents bundled the 78-year-old tycoon into an SUV, as he once more raised his fist to the crowd.

"This is an active crime scene," Secret Service officers told reporters, ordering them out of the area.

"We saw a lot of people go down, looking confused. I heard the shots," said John Yeykal from Franklin, Pennsylvania, who was attending his first Trump rally.

US politicians reacted with shock to the incident.

Former president Barack Obama said there was "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," he said.

Republican minority leader Mitch McConnell added: "Tonight, all Americans are grateful that President Trump appears to be fine after a despicable attack on a peaceful rally. Violence has no place in our politics."

Billionaire Elon Musk reacted by quickly endorsing Trump.

"I fully endorse President Trump and hope for his rapid recovery," Musk wrote on X, which he owns along with car manufacturer Tesla, as he shared a video of Trump pumping his fist while being escorted away.