Police are searching for a driver who picked up a young female hitchhiker who claims an "incident occurred" inside the car.

A 22-year-old woman was hitchhiking between Queenstown and Cromwell on the morning of September 5.

She was picked up near the Frankton cemetery by a man driving a fawn coloured 4WD.

A police spokeswoman said an incident occurred while they were travelling together, but she declined to give further details.

The hitchhiker described the driver as a European man in his 40s. He was clean shaved with short white hair, wearing a black baseball cap and yellow hi-vis vest.

The driver wore a gold band on his left hand, had two car seats in the back of his vehicle for his twin children and a black dog, described as a Labrador, was also in his back seat.

This man drove the woman from Frankton through to Cromwell where she was dropped off.

Police would like to speak with the driver and anyone else who thinks they may have information which may help in this investigation.

Police would also like to hear from anyone who saw the woman near the cemetery in Frankton between 8 and 9am on September 5.

She is European, has shoulder-length dark brown hair and was wearing a checked black and white shirt, black jeans and boots and carrying a black Nike gym bag.

People with information can contact Detective Gary Hyndman at Cromwell Police on 03 445 1999 or Crimestoppers on 0800 555 111.