Several cars have been damaged after stones were thrown onto Broadway from the direction of the Kings Theatre.
Constable Vanessa Paki Paki of Stratford Police says four complaints have been received about the May 9 incident.
Police are reviewing camera footage taken at the time, but were unable to identify anybody involved. She urged people with any information to contact police.
Haley Tecofsky was driving down Broadway at around 8.15pm when she heard a big bang.
A rock had hit the back door of her car, next to where her toddler was sitting, and was just 30cm from hitting the child's window. She says the car had minor damage but the whole incident was upsetting.
"You could be putting somebody's life at risk — they don't think of that.
"It's just the thought of it. Anything could have happened."
Noeleen Palmer of Hawera says her car was damaged at about 8.45pm when she was driving home from a St Mary's School concert. The new car, had only been driven three times, received a dented roof and chipped paint, leaving her footing a $300 excess on her insurance.
She reported the incident to the police and says she is disappointed, especially because it was a new car.
"It's the fright you get — and the fact that you could go over onto the wrong side of the road. It's dangerous."
Noeleen's daughter Christine Evans was following her mother and witnessed the incident. She posted it on social media and discovered they weren't the only ones hit. She says up to six cars were hit by stones between 6pm and 9pm that evening, with two cars receiving smashed windscreens.