Rocks and other items are being thrown from motorway overbridges around Auckland, police say.
Counties Manukau West area commander Inspector Naila Hassan said police were concerned by a recent trend where people had been seen throwing rocks and other items from motorway overbridges.
"Motorists deserve to feel safe on our roads," Hassan said.
"This reckless behaviour from those involved is extremely dangerous and can potentially have fatal consequences."
People needed to remember throwing anything from overbridges posed a serious risk to vehicles and their occupants.
Those responsible could face charges of endangering transport under the Crimes Act, which carries a maximum sentence of 14 years imprisonment.
She asked motorists to be vigilant and to report to police by calling 111 if they spot this type of activity taking place.