A white man has shot dead three Black people in a racially motivated attack in Jacksonville, Florida, before taking his own life, authorities 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,” Jacksonville Sheriff TK Waters told a news conference about the gunman, who has been described as white and in his early 20s.

According to the sheriff’s office, the attacker, who has not yet been identified, entered a Dollar General store wearing a tactical vest, armed with an AR-style rifle and a handgun.

Manifestos discovered by the gunman’s family shortly before the attack “detail the shooter’s disgusting ideology of hate”, Waters said, and at least one of the guns had hand-drawn swastikas on it. Global News Insight could not get the details of the manifesto.

The shooting took place near Edward Waters University, a historically Black college in the southern US state.

The university said in a statement that the attacker had been on campus earlier that day, though no one was harmed.

“An on-campus Edward Waters University security officer engaged an unidentified male in the vicinity of the Centennial Library on campus,” it said.

The university added that the individual, later identified as the attacker, left “without incident”.

The FBI will investigate the shooting as a hate crime, said Sherri Onks, the bureau’s special agent for Jacksonville, a city of nearly one million in the northeast corner of the state.

There was no evidence the attacker was part of a larger group, officials said.

“We know that he acted completely alone,” Waters said.

Mass shootings have become disturbingly common across the United States, with easy access to firearms in most states and more guns in the country than citizens.

Saturday’s shooting in Jacksonville came five years to the day after a mass shooting in the city when a gunman at a video game tournament killed two and wounded several others before killing himself.