A white man armed with a high-powered rifle and a handgun killed three Black people at a Dollar General store in Jacksonville, Florida, on Saturday, before shooting himself, in what local law enforcement described as a racially motivated crime.

"This shooting was racially motivated, and he hated Black people," Jacksonville Sheriff TK Waters told a press conference.

The suspect, whom Waters described as a white male wearing a tactical vest, was not identified. Waters said all three victims - two men and a woman - were Black.

Waters said authorities believed the shooter acted alone, and that before the shooting he had authored "several manifestos" for media, his parents and law enforcement detailing his hatred for Black people.

Waters described his weapons as a Glock and an "AR-15 style" rifle, with swastikas on it, referring to a lightweight semi-automatic long gun often used in mass shootings.

"The hate that motivated the shooter's killing spree adds an additional layer of heartbreak," Waters said.