The decomposing body of a child was discovered in Lenasia, south of Johannesburg, on Tuesday evening, Gauteng police said.
"A passer-by noticed hair protruding from a rock near an informal settlement in Lenasia. He discovered that it was a human body and called the police," said Warrant Officer Kay Makhubela.
The child's body was in a bad state of decomposition, and it was not yet known whether it was a boy or a girl, he said.
A murder docket has been opened. No arrests have been made.