Migrants under attack in South African slums
Police said the injured at the Kya Sands township included migrants from Zimbabwe and Mozambique as well as South Africans.
At least ten people have been arrested on suspicion of assault.
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Hide AdA series of attacks on foreign workers in 2008 killed 62 people. Another wave could wreck the positive image that Africa's biggest economy was able to portray when it hosted the World Cup.
"We are keeping a close eye on the situation," a police official said.
The military have joined about 100 security personnel deployed in the township and about 50 police were on standby, Talk Radio 702 reported from the area.
Tensions have long been growing between South Africans and millions of foreign migrants they accuse of taking jobs and homes. But open animosity appeared to be put on hold during the World Cup as South Africa showed its best face to the world.
Many migrants feared a rapid dissipation of feelings of African unity generated by the first World Cup held on the continent. Many have fled to homes in neighbouring states since the tournament ended earlier this month.
Running battles erupted late on Monday at Kya Sands after a robbery in the township provoked anger between local people and foreigners.