A baby girl has been found dead in a bag thrown into a ditch in KwaThema near Springs, police said on Sunday.

Captain Johannes Rampholo said a passerby saw an orange bag in a water-filled ditch, went to investigate and found the body.

"The baby could be between two and three month olds."

He said it was not clear whether the baby was dead or alive when thrown into the ditch.

Police were investigating a case of concealment of birth, Rampholo said.