JOHANNESBURG, South Africa — Thousands of black immigrants in Johannesburg have fled their homes amid a growing tide of mob violence that has left at least 23 dead and many badly injured.

The mobs, armed mainly with pangas, clubs, and bars, rampaged through townships, squatter camps, and the city center attacking those they suspected were not of South African origin.

Criminal gangs have exploited the unrest to rape and plunder.

The anger was directed mainly at Zimbabweans, who had fled the privations of their home country but endure poor housing, unemployment, and crime.

The mobs hacked at their victims and set others on fire in scenes reminiscent of the township violence of the apartheid years. Up to 6,000 immigrants were reported yesterday to have fled their homes.

Archbishop Desmond Tutu called for the violence to end. Nelson Mandela repeated a plea made during an outbreak of xenophobic violence in 1995: “We cannot blame other people for our troubles.”

Last night, flames and smoke could be seen rising from burning shacks and homes on the outskirts of the city while police stations, churches, and community halls struggled to cope with people trying to escape the violence.

“This is a classic refugee situation and the authorities do not seem to be able to deal with it,” said Rachel Cohen of Medecins Sans Frontiers, which was organizing blankets and food for those who had fled the violence.

The violence erupted last week in the township of Alexandra, where Zimbabwean immigrants were the prime target for a welter of severe social problems.