A 13-day-old baby boy was kidnapped during a house break-in in Kempton Park West, east of Johannesburg, police said on Tuesday.
"They tied the mother and her 16-year-old daughter up and then took the baby, its clothes and the mother's cellphone," Constable Sharon Mahamba said.
The father arrived home after 10pm and untied his wife and daughter.
The robbers were identified as three men and two women.
"When police arrived there were no signs of forced entry; it seems as if they used a key to get in," Mahamba said.
No arrests had been made.
A case of house robbery and kidnapping was being investigated.