JACKSONVILLE, Aug 25 (CNA) - A gunman driven by racial hate shot and killed three Black people in Jacksonville, Florida on Saturday (Aug 26) before fatally turning the gun on himself, authorities said.

The shooter, a white male in his early 20s, was outfitted with a tactical vest and armed with an AR-style rifle and a handgun when he started firing inside a Dollar General discount store, Sheriff TK Waters said.

"He targeted a certain group of people and that's Black people. That's what he said he wanted to kill. And that's very clear," the sheriff said, adding there were two male victims and one female victim.

Manifestos discovered by the gunman's family shortly before the attack "detail the shooter's disgusting ideology of hate", Waters told a news conference.

The FBI would investigate the shooting as a hate crime, said Sherri Onks, the bureau's special agent for Jacksonville.

The shooting was the latest in a spate of gun violence this weekend in the United States, following deadly outbursts in Boston, Chicago and Oklahoma.

The Associated Press reported that the shooter left behind writing that led investigators to believe that he committed the shooting because it was the fifth anniversary of when another gunman opened fire during a video game tournament in Jacksonville, killing two people before fatally shooting himself.

The shooting happened just before 2pm near Edward Waters University, a small historically Black university.

Edward Waters University students were being kept in their dorms, the school said in a statement. No students or faculty are believed involved, the school said.

Penny Jones told The Associated Press that she worked at the store until a few months ago. She lives a few blocks away in the predominantly Black neighbourhood.

“I’m just waiting to hear about my co-workers that I used to work with,” Jones said. “I don’t know if it’s safe to move about the neighbourhood.”

Jones added that she was "feeling awkward, scared".

"I don’t want to leave my house. I’m thinking, do I want to go back to the store? Is this going to start happening more frequently? I don’t know what the cause of it is. I’m confused. It’s a lot of different feelings going on right now,” she said on Saturday afternoon.