The shooting took place at Mac's Lounge in Hartsville, Darlington County Coroner Todd Hardee told news outlets. The two victims were identified as Dicaprio Collins, 21, and Bryan Robinson, 29, according to the coroner's office.
There was not any immediate information about what led to the shooting. The South Carolina Law Enforcement Division and the U.S. Marshals Service were assisting Hartsville police with the investigation.
According to its Facebook page, Mac's Lounge also serves as a music venue. Hartsville is about 25 miles (40 kilometers) northwest of Florence, South Carolina, and about 40 miles (64 kilometers) south of the North Carolina state line.
A witness, interviewed by WMBF, described a chaotic scene as bar patrons ran for their lives.
Samuel Dupree told the station he was dancing when he heard something that at first sounded like a firecracker, but he turned and saw the gunfire. He said people in the bar were rushing toward the exit.
"People were trying to get through that tiny door and they couldn't," he said. "I helped someone up off the ground I saw get trampled. I'm not going to let this person just died from getting run over."