Members of the heavy metal band Damageplan had just begun their first song at the Alrosa Villa when the man opened fire, initially targeting guitarist "Dimebag" Darrell Abbott, a witness said.
Police say Abbott was among those killed in the rampage.
Abbott, one of metal's top guitarists, and his brother, Damageplan drummer Vinnie Paul Abbott, were original members of thrash rock pioneers Pantera, one of the most popular metal bands of the early 1990s.
The witness, 22-year-old Chris Couch, said he was standing about 30 feet away from the stage when he noticed a man wearing a hooded sweatshirt and hockey jersey walk up to the stage, followed by a bouncer and another club employee. The man in the jersey climbed onto the stage, started yelling and shot the guitarist five or six times at close range, Couch said.
"He was just shooting. Just shooting. He was kind of standing behind a big stack of speakers and he was bang, just shooting," an eyewitness said.
"It kinda sounded like a cap gun," another witness said. "And he was shooting people and there were still people just hanging around thinking it's a hoax."
Couch said the gunman also shot a bouncer who pulled him off the musician.
Columbus police spokesman Sgt. Brent Mull said that after shooting at members of the band, the gunman fired into the crowd. Mull said a police officer who arrived shortly after the shooting began shot and killed the gunman.
"If the officer wasn't as close as he was, I think this would have been a lot worse," he said. "It was a chaotic scene, just a horrific scene."
Mull said more people could have been shot and left the scene before authorities arrived.
"It's a concert hall that is known in Columbus for trouble. It's had a series of shootings in the past," Reporter Kevin Landers of CBS affiliate WBNS-TV reports. "Apparently, there were bouncers in the music hall, but there were not uniformed police officers working this event."
After the shooting began, Couch and a friend headed for the exit along with a tide of hundreds of fans.
"It was definitely a grudge. It was against something," Couch said.
Amanda Stankus, 19, who attended the show with Couch, said she initially thought the shooting was part of the show. "I just saw the guitarist fall down, and we decided to get out of there," she said.
Other members of Damageplan include vocalist Patrick Lachman and bass player Bob Zilla, according to the band's Web site.
A message left with Atlantic Records, which oversees the record label on which Damageplan records, was not immediately returned.
Damageplan's Web site said Darrel and Vinnie Abbott grew up in the Dallas-Fort Worth, Texas area where their father Jerry Abbott owned a recording studio. Another entry on the site lists the elder Abbott as a country-western songwriter.
Telephone numbers for both Darrell and Jerry Abbott are unlisted and could not be reached early Thursday by The Associated Press.
Pantera, known for its brutally hard, fast and aggressive sound, recorded four albums between 1990 and 1996. They attracted a massive cult following and the band's third release, "Far Beyond Driven," debuted at No. 1 in 1994, surprising chart-watchers and critics alike.