A truck driver stopped to assist the driver of a four-wheel-drive that flipped on State Highway 1 north of Whangarei yesterday.

The driver of the flipped vehicle escaped uninjured.

Police were called at noon to the scene of the accident on the state highway, about 1km north of Hikurangi, where the 4WD vehicle - towing a trailer laden with timber - had flipped over, blocking the northbound lane.

The driver was out of the vehicle when police arrived and had minor scratches. He did not require an ambulance. It appeared the 4WD and trailer had jack-knifed, causing the rollover. Police are investigating the crash.