Tourists were left shocked when they spotted two young men urinating out the windows of a moving vehicle at high speed on a motorway.

Angela Chilton, from Essex in England, and her husband Karaan Chilton were travelling along a Southland highway in New Zealand when they noticed the reckless behaviour on Monday morning.

The couple saw the passengers hanging half their bodies out the side windows of the silver car as the driver travelled on a 100kmh speed limit road.

Two young men were caught allegedly urinating out the windows of a moving car at high speed on a motorway

'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 told NZ Stuff.

Mrs Chilton said they noticed one of the passengers had leaned out of the window up to four times while the other person on the opposite side appeared once.

The pair were travelling behind the vehicle for about 10 minutes on the State Highway 6 between Garston and Athol when the passengers appeared to urinate while several cars drove past.

Tourists saw the passengers hanging half their bodies out the side windows of the silver car on Monday

The pair travelled behind the vehicle for about 10 minutes on the State Highway 6 between Garston and Athol

Mrs Chilton said her husband was driving at 100kmh at the time and they estimated that the vehicle in question was travelling a bit faster than them.

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.