People have been riding dirt bikes recklessly and dangerously on public roads and in reserves in Auckland, prompting a police investigation.
Counties Manukau's Senior Sergeant Jono Chappell says they're aware of several recent incidents involving anti-social and dangerous behaviour from dirt bike riders.
In some incidents, the bikes are being ridden "recklessly" on the roads and can have "serious and fatal consequences".
"The way in which some of these bikes are being ridden is extremely dangerous," Mr Chappell says.
"This behaviour is creating unnecessary risk for the riders themselves and members of the public."
Dirt bikes need to be registered if they're being ridden on public roads, with riders needing to wearing a helmet and have an appropriate licence if the bike is over 50cc.
Anyone who's witnessed dangerous behaviour is asked to contact police, including telling them the time and place it's occurring.
Photos are also helpful, Mr Chappell says.
"This behaviour is dangerous and has had serious and fatal consequences in the past."
Information can be provided to police on the non-emergency number 105, or anonymously via Crimestoppers on 0800 555 111.