The spate of killings has unleashed a wave of public anger at the police for failing to tackle high levels of violent crime.
"It was such a brutality," Police Minister Bheki Cele told a crowd gathered in Soweto's Orlando East neighborhood. "These people really came to kill and destroy. We don’t know their motive but I guarantee we will find them."
The high number of rounds used in Soweto - forensic teams found 137 AK-47 cartridges at the crime scene - meant the killers would have had to reload while in middle of the slaughter, he said.
Meanwhile, police confirmed a second shooting hours earlier on Saturday, in a tavern in Pietermaritzburg, 500km (300 miles) southeast of Soweto, that killed four and wounded eight.
On Thursday, during a suspected robbery in a tavern in Katlehong, outside Johannesburg, two were killed and two others wounded.
The three attacks are not believed to be linked.
Around 20,000 people are murdered in South Africa every year out of a population of about 60 million.
There are about 3 million guns registered in the country, according to campaign group Gun Free South Africa, though many more are thought to be circulating on the black market.
