A Southland district police spokesman said police were aware of the incident and were currently making enquiries.
"This behaviour is not only irresponsible but extremely dangerous for both the occupants of the vehicle and any other road users.
"Police continue to urge any motorist who witnesses any dangerous behaviour by any road user to contact police."
Road user safety adviser for Road Safety Southland Maureen Deuchrass said the passengers were putting their lives - and other motorists on the road - at risk.
"I think there's enough to worry about on our roads without worrying about this kind of stupid behaviour," he said.
Marty Oetgen, one of the owners of NZ Rent a Car, confirmed the company owns the car in which two passengers were spotted on State Highway 6 on Monday morning.
The car was hired in Christchurch by a 22-year-old French man on February 10 and was due back tomorrow.
"We go through a formal process before handing the keys over.
"This particular man had lived in Australia and so was familiar with driving on the left-hand side of the road and he assured us he'd read the [New Zealand Transport Agency] and DriveSafe websites.
"Urinating out of a vehicle ... That's not something you can pre-empt."
Mr Oetgen said they had made several attempts to contact the man directly but his phone went to answerphone.
"It's dangerous and irresponsible from our point of view. There isn't a lot we can do but we did contact police and we're certainly interested in what he has to say tomorrow."
A spokeswoman for Embassy of France said they were aware of the incident but had nothing to say on it.
•Motorists who witness dangerous behaviour by road users can contact either *555 or in an emergency, 111.
