Relieving Auckland City District Commander inspector Jacqui Whittaker said a vehicle that was part of the parade appeared to have experienced a mechanical malfunction and rolled slowly into two pedestrians who were standing in front of the stage.
The pedestrians were moderately injured.
"Unfortunately, a small group of people took it upon themselves to retaliate, and three people - including two children - were pulled from the vehicle and assaulted," Whittaker said.
"Three people received minor injuries but were not transported to hospital."
Police were working to identify those responsible for the assault and determine what occurred.
"We understand this was an unsettling event, where multiple people have become injured, and not the end to the parade which was wanted. However, police want to send a clear message - please do not take matters into your own hands," Whittaker said.
"As this incident demonstrates, something may not be what it seems to you at first, and others stepping in can result in unnecessary injuries and further distress."
Tensions were high after the Great North Rd incident, which happened about 11.45am, and it is understood the crowd jumped on the bonnet of the car and smashed their fists on it and that Māori wardens had to hold them back.
NZME’s Michael Burgess was at the parade and said two purple BurgerFuel muscle cars were travelling down Great North Rd.
"They were revving a lot. As they got to the end, [one of the drivers] tried to do it again.
Burgess said several people were knocked over in the car.
"Everyone descended on his car, you know."
"There were lots of kids lining the streets, lots of great floats had come past and then … there was just this sickening sound, the screams," Burgess said.
"Just the shock in the air and the reaction was a mix of just shock, anger and disbelief, everyone standing there, it’s just something you just don’t see."
A member of the band told the Herald a woman who was injured was hit from behind while filming the band.
Nikki Soons, BurgerFuel NZ head of brand and marketing, said: "We are shocked to hear about the incident that has occurred involving one of the BurgerFuel promotional vehicles and we are very concerned for anyone injured. We do not yet know what caused the accident and are currently gathering all the information. We have a BurgerFuel representative at the scene and will be working with police to ascertain what has happened."
Paramedics treated six people.
The driver of the car was seen getting into a police vehicle. A police spokesperson told the Herald they were speaking with the driver.
"Initial information suggests the car experienced a mechanical fault prior to the crash, inquiries are ongoing to determine the full circumstances of the crash."
It’s the suburb’s first Santa parade and was set down to run from 11am to 2pm with food and music.
Parade floats were to leave from the Avondale Racecourse at 11am, travel up Elm St to Rosebank Rd, and to Great North Rd where participants were to join in on the festivities in the main street below Avondale Primary School.
BurgerFuel has a fleet of custom, classic and muscle cars from between 1965 and 1972 that are used for various events.