Law enforcement officials told a news conference that they apprehended a suspect who was spotted by Secret Service agents with an AK-47-style assault rifle outside the Trump National Golf Course. Secret Service agents fired shots, and the suspect fled in a black SUV.
"The FBI has responded to West Palm Beach Florida and is investigating what appears to be an attempted assassination of former President Trump," the agency said in a statement.
Trump's campaign had earlier said he was safe following gunshots in his vicinity but gave no details.
The Secret Service said it was investigating the incident, which occurred about 1:30pm on Sunday (local time).
Trump sent an email to his fundraising list saying there were "gunshots in my vicinity, but before rumors start spiraling out of control, I wanted you to hear this first: I AM SAFE AND WELL!" according to an email seen by Reuters.
Trump was injured in an assassination attempt in Pennsylvania on July 13, raising questions about protection for candidates just months ahead of what looks likely to be highly contested November 5 election in which he will face off against Democratic Vice President Kamala Harris.
The White House said in a statement that President Joe Biden and Vice President Kamala Harris had been briefed about the incident and were relieved to know that he is safe.
"Violence has no place in America," Harris said in an X social media post.
The Washington Post said Trump had been golfing at the course when the incident occurred. Secret Service agents took him to a holding room at the club, it said, citing two people briefed on what had happened.
Trump campaign spokesperson Steven Cheung did not immediately respond to requests for comment.
The first shooting of a US president or major party presidential candidate in more than four decades was a glaring security lapse that forced Kimberly Cheatle to resign as Secret Service director under bipartisan congressional pressure.
Trump was grazed in the right ear and one rallygoer was killed in the gunfire. The gunman, identified as a 20-year-old Thomas Crooks, was shot and killed by a Secret Service sniper.
The US Secret Service's new acting director said in August that he was "ashamed" of a security lapse that led to the assassination attempt.