Christchurch police have impounded 15 cars as they attempt to crack down on thousands of car enthusiasts descending on the city for the biggest motoring event of the year.
The annual 4 & Rotary South Island Championships are being held this weekend, bringing with it a deluge of boy racers.
On Friday night, 70 police, along with vehicle inspectors and court staff, targeted illegally modified vehicles and driver behaviour.
They say 15 boyracers had their cars impounded for unpaid fines or illegal modifications.
A large number of infringement notices were also issued for driving and speed offences.
Police intend to continue the crackdown on Saturday night, maintaining high visibility policing, and targetting speeding, drinking, and other what they call "trauma-promoting offences".
The local Boyracers United group says events will still take place despite the police trying to control their activities.
During each 4 & Rotary event held in Christchurch, thousands of cars drive around the city on the the Saturday night in an organised convoy.