A deputy sheriff's son killed two people and wounded four others at Florida State University before he was shot by officers and hospitalised, authorities have said.
Police believe the 20-year-old suspect - the son of a Leon County sheriff's deputy - acted alone and a motive is not known.
The suspect had access to his mother's handgun, which was once her service weapon.
She bought it from the police department and it is now a personal firearm, authorities said.
"Unfortunately, her son had access to one of her weapons that was found at the scene," Leon County Sheriff Walter McNeil said at the press conference.
The suspect, identified as Phoenix Ikner, was believed to be a student at FSU in the state capital of Tallahassee, said Jason Trumbower, chief of the university's police force.
The two people who were killed were not students.
Mr Trumbower did not provide details on the four others who were shot and wounded.
Responding police officers shot the suspect when he failed to obey orders to surrender and took him into custody, authorities said.
The four wounded victims, plus Mr Ikner, were taken to the hospital with gunshot wounds.
The shooting started about 11:50am local time (4:50pm Irish time) near the student union building on the FSU campus.
Students and faculty were told to shelter in place as police responded. More than 42,000 students attend classes at the main campus.
Student Max Jenkins described the shooter leaving the student union building and firing four or five shots outside.
"He saw the maintenance guy who was waving everybody and I guess heard him probably and turned and shot that way," Mr Jenkins said in a video on the Tallahassee Democrat newspaper website.
"There's a golf cart over here with a bullet hole in it," he added.
Chris Pento was on a tour of the university with his children and eating lunch at the Student Union building when shots started ringing out.
"It was surreal, people started running. She just got trampled over," Mr Pento told local TV station WCTV, referring to his daughter.
In addition to the handgun, authorities believe the suspect brought a shotgun onto campus but said it was uncertain if that weapon was used in the shooting.
My team and I have been briefed on the tragic shooting at Florida State and our FBI Jacksonville team is on the ground assisting. We will provide full support to local law enforcement as needed. Please keep the FSU community in your prayers.
— FBI Director Kash Patel (@FBIDirectorKash) April 17, 2025
FBI Director Kash Patel said in a post on X he had been briefed on the shooting and that a team from the Jacksonville FBI field office was assisting.
"We will provide full support to local law enforcement as needed," he added.
US President Donald Trump said he had been briefed on incident and that he would provide an update about the situation later.
"It's a shame, a horrible thing, it's horrible that things like this take place," he said.
This incident was the second shooting on the FSU campus in 11 years.
In 2014, a Florida State University graduate opened fire at the school's main library, wounding two students and an employee as hundreds of people were preparing for exams.
Other mass shootings on college or universities in the US in recent years include the 2007 Virginia Tech massacre in Blacksburg, Virginia, where 32 people were killed and 23 injured.
In 2023, there were two college mass shootings, one at Michigan State University, where three students were killed and at least five others injured.
The other incident unfolded at the University of Nevada, Las Vegas, where three faculty members were killed before a suspect died in a shootout with the police.
