Neighbours of house number 1178 in Tau Street, Thabong in the Free State awoke early on Friday morning to panicked screams.
They promptly went outside and found the shack on fire.
Residents tried to extinguish the fire and called firefighters, but despite their efforts, the three neighbours died in the fire, said Brigadier Motantsi Makhele.
The bodies found were identified as a 20-year-old mother and her two daughters, aged four and one.
A case of inquest has been registered for further investigation, Makhele confirmed.