Police are investigating reports a group of men arrived in a minibus taxi and opened fire on some of the patrons at the bar late on Saturday night.
Police were on Sunday morning removing the bodies of the deceased and investigating what had led to the mass shooting.
Those injured were taken to Chris Hani Baragwanath Hospital.
The number of cartridges found on the scene indicates that a group of people opened fire in the bar, Gauteng province police commissioner Lieutenant General Elias Mawela said.
"The primary investigation suggests that these people were enjoying themselves here, in a licenced tavern operating within the right hours," Mawela told The Associated Press.
"All of a sudden they heard some gunshots, that is when people tried to run out of the tavern. We don't have the full details at the moment of what is the motive, and why they were targeting these people.
"You can see that a high calibre firearm was used and it was shooting randomly. You can see that every one of those people were struggling to get out of the tavern."
The area where the shooting took place was very dark, making it harder to find people who could identify the suspects.
Rifles and a 9mm pistol were used in the attack, national police spokeswoman Colonel Dimakatso Sello said.
The shooting in the Soweto bar comes two weeks after 21 teenagers were found dead in a tavern in the city of East London.
The cause of those deaths has not yet been announced by authorities, but the teens were not shot nor crushed in a stampede, according to officials.
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