A driver on State Highway 6 in Southland was shocked with what appeared to be two men urinating from a moving vehicle.

The actions of two car passengers who appeared to lean out a car window to urinate while travelling at 100kmh on a Southland 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.

Angela Chilton Two passengers hanging from a moving vehicle on SH6.

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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.

They were behind the car for about 10 minutes during which several vehicles passed the car in question some while one of the passengers was hanging outside of the car.

Chilton said her husband was driving at 100kmh along the stretch of road and estimated the other vehicle to be travelling a bit faster than them.

She was worried not only for the passengers' safety, but for others on the road and noticed other drivers and passengers looking back at the car in question.

"They were going at such a speed," she said.

"I said to my husband just don't get any closer because if they fall out we don't want to run them over."

She took some photos of the incident but did not call *555 as she was not aware such a service existed.

"If I had known that we would have dialled it," she said.

Chilton said the vehicle turned off SH6 on to SH97 at Five Rivers heading towards Mossburn and assumed they were tourists heading to Milford.

She said the vehicle was a rental car.

Road user safety adviser for Road Safety Southland Maureen Deuchrass condemned the behaviour and was disappointed at the passengers' lack of sensibility.

"They're putting their lives at risk and others' lives at risk," she said.

"I think there's enough to worry about on our roads without worrying about this kind of stupid behaviour."

Deuchrass said it didn't matter whether they were tourists or not, their behaviour was not something other motorists needed to put up with and it was a distraction on the road.