Police spokesman Vuyo Mhaga confirmed to AFP that a case of assault had been opened against higher education deputy minister Mduduzi Manana.
The incident occurred yesterday at the upmarket Cubana club in Johannesburg's Fourways district.
"As we were leaving we were assaulted by Deputy Minister Manana and his group of friends," one of the victims told the eNCA television channel.
"They kicked me, they punched me as well as my cousin."
A journalist with the public broadcaster, Lumko Jimlongo, witnessed the incident.
Manana "was pulling her by the hair while she was still on the floor," he added.
Police Minister Fikile Mbalula said the allegations were "disturbing" and vowed that the case would be fully investigated.
"No one is above the law irrespective of their position in society," he said.
The ANC expressed "great disappointment" at the alleged actions of one of its ministers.
The main opposition Democratic Alliance party called on Manana to apologise and resign.
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