"It is barbaric. The reason [for the attack] is said to be people vying for jobs eliminating each other," ANC spokeswoman Pumla Mtyeku said.
Police Superintendent Wikus Weber said several men, armed with assault rifles and handguns, opened fire on a line outside the N.F. Die-Casting factory at Alrode, a few kilometers from the city center just before 3 a.m.
"It was savage ... we expect the death toll to rise," Weber said. He said some of the people were very badly hurt.
Officials had said 10 people had been killed, but police said later although at least two of the 23 wounded were not expected to survive, the death toll remained at eight.
Survivor Buthelezi Mtatshelwa, wounded in the chest, said at a Johannesburg hospital that he had no idea why he had been shot.
"I was looking for a job, but I am not going to go back to that place again," he said from his hospital bed.
The company, which is owned by the giant Anglo American Corporation, would not comment on a motive but said about 200 people had gathered outside the factory looking for jobs when the gunmen struck.
Union officials said the company had been on a recruiting drive and had been issuing numbered interview tickets to job seekers.
They said some tickets had been stolen the previous week, forcing the company to re-issue tickets early Monday. The attack appeared to have aimed at deterring jobseekers, they said.
Weber said the gunmen walked up to the line and opened fire without warning. Some of the victims, bleeding from bullet wounds, staggered up to a kilometer from the scene before collapsing.
Hours after the incident, pools of blood, discarded shoes and spent bullet casings were all the evidence left.
Police, who said it was too early to comment on a motive, said the gunmen had fled on foot. Road blocks had been set up and police helicopters were searching for signs of the gunmen. Both attackers and victims were black.
Unemployment is running at about one third of South Africa's economically active population, prompting fierce competition for work. If the killings were jobs-related they would be the first of their kind in the post-apartheid country.
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