A tourist driver has been punched in the face after another motorist signalled for him to pull over and removed his keys.
Police said the man had been driving a white Toyota rental car on Main South Rd in Greymouth when a motorist in a silver sedan signalled for him to pull over near the Australasian Hotel.
Police understand the man went to the driver's window, removed the keys from the car, abused the driver and punched him in the face.
Members of the public stopped to help the injured man and brought him to the police station.
Constable Damon Monks said the victim suffered bruising to his eye. Both he and his female passenger were shaken by the incident.
Police want to identify the man involved. He was described as a 35- to 45-year-old man, about 1.75m tall, with dark skin and a round face. He had been driving an older model silver sedan.
Police warned members of the public against taking matters in to their own hands.
Mr Monks said anyone who had concerns about driver behaviour should contact police with the vehicle's registration details and the matter would be followed up.
Police would like anyone who witnessed the incident or could identify who was involved to contact Greymouth police on 03 768 1600.
Information could also be given anonymously by calling Crimestoppers on 0800 555 111.