Dozens of bikers took over the streets of Auckland on New Year's Eve, executing dangerous manoeuvres and damaging a police patrol car.
The stunts were considered so dangerous, police chose not to intervene.
"We have already received a number of complaints regarding the extremely dangerous driving behaviour being carried out by some of the riders," Acting Inspector Terry Lee said.
"They have also deliberately smashed a police patrol car wing mirror."
The spokesman said that with a group this size it was not practical for police to intervene as it would cause significant risk to other road users and police staff.
Videos sent to the Herald showed the motorcyclists performing wheelies, burning rubber and spinning their bikes dangerously.
In another video filmed at Hollyford Drive in Manukau around 11.15am, the bikers could be seen riding on the footpath with police trailing alongside on the road with their sirens going.
Police said they were now making inquiries of the dirt bikers who left Ōtara this morning and were driving around the city.
The group has now dispersed.
Lee said police were aware in advance of the ride and had a number of staff monitoring the situation.
"Our community can be assured that we will be following up on these matters and holding people to account for their dangerous driving," he said.
Witness Connie Miller, who has written an email to police, said the bikers also rode their bikes along Tamaki Drive and had blocked the roads early this afternoon.
"Many riders appeared to be under the legal age to even hold a motorbike licence and most weren't wearing helmets," she said.
Miller said many of the bikes looked to be "not warrantable" and "failed to meet any registerable standards".
"They rode on both sides of the road, performed wheelies, spun their back wheels and blocked oncoming traffic," she said.
"The bikers were so proud of themselves that they even had riders stop in the middle of the pedestrian crossing to film their antics.
"To my absolute disgust, a police car followed them as an escort."
Another Auckland driver, Alyson de Marco, said she had a similar encounter with bikers on Monday along the Southern Motorway.
"A number of bikers with red, weaving in and out, and a number of cars with men sitting outside of the cars on the windows, they then slowed the motorway down to 40km," she said.
"[There was] absolutely no sign or intervention from the police despite many traffic cam [footage]. Slowly the gangs are exerting their hold over Auckland."
Motorists are being warned to expect hazardous driving conditions.