Wellington  - A mother tipped off police to arrest her son on a rape charge after seeing her kitchen knife, which he allegedly used in the attack, in a photograph released by investigators, a newspaper reported on Saturday.

Police released a photograph of the knife and a tea towel found near the scene of the attack on a 22-year-old Dutch tourist to the local Southland Times, which posted it on its website.

The woman recognized the items when visiting a friend who opened up the photograph on her computer as they talked about the attack in Tuatapere, 90 kilometres north-west of Invercargill, on Thursday, the paper said.

The woman called the police, who arrested her 25-year-old son and charged him with raping the tourist at knifepoint as she and her partner slept in their vehicle in a camping ground. (dpa)