South African police said on Tuesday a government minister was robbed and her bodyguards had their guns stolen in what authorities in the crime-ridden country described as an "unprecedented incident".

The attack took place on Monday as Transport Minister Sindisiwe Chikunga was travelling on a highway south of Johannesburg, police said.

"Personal belongings and two SAPS (South African Police Service) service pistols were stolen," said police spokeswoman Athlenda Mathe.

"A manhunt has since been launched following this unprecedented incident and to bring to book those responsible."

Local media reported that the vehicle the minister was travelling on had stopped to change a punctured tyre when the robbery occurred.

Involving a high-profile official with an armed security detail, the incident is striking even for South African standards.

The country has long had a reputation for violent crime and is often described as one of the most dangerous in the world outside a war zone.

Authorities have been accused of failing to ensure safety and secure justice for crime victims.

"The SAPS is committed to executing its mandate of protecting the executive of the country and community at large," said Mathe.

"VIP protection is one of the key priority areas for the SAPS and has been undertaken with excellence over the years."