Gunmen opened fire on a group of men playing dice on a street corner in a Johannesburg suburb, killing four of them and injuring two others, police said Sunday.

The attack on Saturday evening in Lenasia came a week after two separate shootings killed 20 people - 16 at a bar in nearby Soweto and four others at a tavern in South Africa's eastern city of Pietermaritzburg.

"Preliminary investigation suggests that a group of men were playing dice at a street corner at approximately 7:30 pm (1730 GMT) when they were attacked by unknown assailants who shot at them," police said.

"Four people were certified dead on the scene, while two people were taken to the nearest medical care center after sustaining gunshot wounds."

Regional police chief Elias Mawela called the crime scene "horrific" in the southern suburb of South Africa's economic capital.

"They were seated. They were attacked for no apparent reason," he said.  An investigation has been launched and police said they had launched a manhunt for the perpetrators.

Shootings are common in South Africa, which has one of the world's highest murder rates, fuelled by gang violence and alcohol.