Young drivers are more likely to crash if they have friends along for the ride.
The risk of a fatal accident involving a young driver can be 10 times greater if there are passengers in the car.
The New Zealand Transport Agency this week started a series of advertisements aimed at young passengers as statistics make clear the danger they can pose.
Singing and sharing gossip are some of the behaviour the agency says can result in a young driver being dangerously distracted.
NZTA road safety director Ernst Zollner said evidence showed the risk of a fatal crash was increased for young drivers if they had passengers in the car.
Compared with driving alone, the risk was 10 times greater if there were two or more passengers. The risk was at its greatest when the passengers were of a similar age to the driver.
Mr Zollner said young people could see the car as a "place to hang out" with friends. The campaign aimed to stress the message that you don't have to be driving to cause a crash.
"Even simple and seemingly harmless things like turning up the music volume or yelling at your mates can badly affect a young driver's ability to concentrate," he said.
Other examples given by the NZTA include talking loudly, expecting the driver to engage in conversation, and messing with vehicle controls such as mirrors or lights.
The campaign includes street posters and print ads with the slogan "Fun can go bad quickly, be a passenger, not a distraction".
The director of road safety charity Brake, Caroline Perry, said the focus of the new campaign was warranted.
"Passengers can be a distraction. Some also encourage the driver to take risks or show off. It's really easy to be distracted but on roads distractions can be fatal. It is essential when you're a passenger in any vehicle - but particularly with a young driver - that you do all you can to minimise distractions and make sure you all get home safely."