An illegal street racer gathering in Waikato was publicised on social media as a "Hamilton invasion" and attracted hundreds of people from outside of the region, police say.
More than 1000 drivers blocked roads across Waikato, resulting in twelve arrests and about 220 infringements on Saturday night.
Hamilton City Area Commander Inspector Will Loughrin told Checkpoint that two people taking part in the racing activity were also stabbed on State Highway 27 in the Matamata area shortly after 12.30am.
"Both of those victims were hospitalised and our ... detectives are following up on that in terms holding those involved accountable."
People came from all over the North Island after seeing an online call to gather, Loughrin said.
"This was a social media call out, so we had people travel to the Waikato from all over the North Island," he said.
"Our police team were engaging with people who had come into the district from Auckland, Bay of Plenty, New Plymouth, Palmerston North, from many places across the North Island, with the intent to be involved in this criminal offending which is really disappointing."
Loughrin said some drivers towed trailers of tyres for burnouts and the amount of risky and criminal behaviour was alarming.
"They referred to it as the Hamilton invasion, so what's different is we had a significant number of people come into the district who don't reside here. But what we've seen is more and more antisocial and criminal behaviour."
He said people were wearing balaclavas in vehicles to avoid being identified, driving without license plates, some failed to stop for police and people seen hanging out of windows of cars driven at speed.
"We've seen a video surface just from the last couple of hours of a vehicle striking someone, so we're just following up on that this afternoon.
"Also of concern is the volume of bystanders standing around putting themselves at risk when these vehicles are carrying out a burnout or racing down the road at speed."
This included one car of teenage spectators, one of whom had brought along their baby.
Loughrin said the driver of the car had been suspended from driving and was issued an infringement notice.
"Our police team dealt with a vehicle full of teenagers and a young baby.
"That baby, one of the parents was in the vehicle, and they'd come over from another district as bystanders to watch this event, which was really concerning because the other part to that was the driver of that vehicle was also suspended," he said.
"There's a number of risks there, that driver shouldn't have been driving but also they'd decided to bring a baby to such an event as this, which poses a lot of risk."
There were seven arrests made for excess breath alcohol, two for disorder, one for driving while suspended, one of a breach of home detention, and another had an existing warrant for arrest."
Police also issued a number of infringement notices to bystanders who were consuming alcohol within liquor ban areas and three people had their licenses suspended
Loughrin said there were a number of unsafe behaviours observed by officers.
As well as the baby found in a vehicle, there were many people in attendance with children, he said.
"We know the community is sick and tired of this behaviour and people who needlessly put others at risk," Loughrin said.
"We want to send a message to anyone involved in this type of behaviour that police will work incredibly hard to hold you to account for any illegal activity - either at the time or after the fact."
Police will be utilising tools such as CCTV and witness accounts to follow up any other criminal offending.
"We're piecing it all together and that will allow us to identify vehicles that have been involved in offending, that we will subsequently impound," said Loughrin.