The actions of two car passengers who appeared to lean out a car window to urinate while travelling at 100km/h on a New Zealand highway are being condemned.

Angela Chilton, from Essex in England, is holidaying in New Zealand with her husband, former Invercargill man Karaan Chilton, and noticed two passengers in the vehicle ahead of them hanging out of the windows when they were travelling on State Highway 6 between Garston and Athol mid-morning on Monday.

The couple saw the passengers, one of them numerous times, lean out of the car window at waist level and said they appeared to be urinating from the vehicle.

She said one of them popped out the car "three to four times" while the other passenger on the opposite side stuck himself out of the window once.