Thirteen people including two children sustained minor burns when a building caught alight in Johannesburg central on Friday, emergency services said.

Spokesman Percy Morokane said a five-year-old boy and his sister, aged four, were home alone when the a block of flats, Matroosberg on Twist Street, caught fire around 3.15 pm.

"They were rescued by firemen and sustained minor injuries. It's not clear where the parents were."

Morokane said the fire began on the ninth floor of the building and spread to the tenth. The 11th floor sustained smoke damage.

"Six of the injured including the children were taken to Hillbrow Clinic and Charlotte Maxeke Hospital. The other seven refused medical attention."

Morokane said the cause of the fire was niot known.