Police found a baby in a vehicle at a street racer event in the Waikato where more than 200 infringement notices were issued, they said.
More than 1000 drivers blocked roads and exhibited unsafe driving behaviours across Waikato overnight, police said.
Twelve people were arrested and about 220 infringements given.
“Alarmingly, attending police found a baby in one of the vehicles driven by a group of teenagers believed to have travelled from out of district,” Hamilton City Area Commander Inspector Will Loughrin said.
“Operation Shadow was a police operation focusing on activity in Hamilton City and the wider Waikato region, targeting illegal street-racing offenders.
“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.
Three people had their licenses suspended.
Loughrin said there were a number of unsafe behaviours observed by officers.
“There were numerous instances of people blocking intersections - both pedestrians and vehicles - a number of vehicles with no number plates and people wearing balaclavas in direct attempts to hide their identities, and people seen hanging out of windows of cars driven at speed.”
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.”
Two people taking part in the racing activity were also stabbed on State Highway 27 in the Matamata area shortly after 12.30am, police said.
Police will be utilising tools such as CCTV to follow up any other criminal offending.