The Miss South Africa beauty contestant at the centre of a nationality row has withdrawn from the competition, saying she decided for her and her family's safety and well-being.

Chidimma Adetshina's announcement on Instagram came a day after a preliminary investigation by the Home Affairs Department found that her mother may have committed "identity theft" to become a South African national.

Ms Adetshina - a 23-year-old law student - said she was born in Soweto, a township next to Johannesburg, and grew up in Cape Town.

In media interviews, she explained her father was Nigerian and her mother was a South African of Mozambican descent.

For weeks her roots have been at the centre of a social media storm, with some South Africans questioning whether she was a South African.

As the row escalated, the organisers of the Miss South Africa pageant asked the Home Affairs Department to conduct an investigation ahead of the event on Saturday.

In a statement on Wednesday, the Department said it had so far found that the identity of an "innocent" South African mother "may have been stolen" by Ms Adetshina's mother.

However, Ms Adetshina "could not have participated in the alleged unlawful actions of her mother as she was an infant at the time", the department said.

It added that it was conducting further investigations to press criminal charges, while also obtaining legal advice "on the implications of the alleged fraudulent activity on Adetshina's citizenship status".

In an Instagram post, Ms Adetshina did not respond to the findings, but said she had taken the "difficult decision" to withdraw from the competition.

She said she was grateful "for all the love and support" she had received, and wished the remaining contestants the best.

"Whoever wears the crown, represents us all," Ms Adetshina added.