A young girl was sexually assaulted in broad daylight while visiting the South Australian Museum in Adelaide.

The four-year-old was in the rear courtyard of the museum's ground floor when the incident occurred Sunday afternoon.

Child Exploitation Section detectives are hunting for a clean-shaven Caucasian man in his late 20s to early 30s with short dark hair.

Mark Judd, the South Australiam Museum's head of public programs, said it was not the first incident at the museum, but that staff were trained to be on the lookout for people "loitering."

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