One person was found in critical condition and taken to hospital.
Wilson said police understood there were “several other parties present” during the alleged assault.
“We are asking anyone who has not yet spoken to police to please come forward and speak with us so we can continue to build a picture of what has occurred.”
Anyone with information should call 105 and quote file number 240621/4014, speak to staff at Kawerau Police Station or leave an anonymous tip by calling Crime Stoppers on 0800 555 111.
It’s understood the incident occurred outside a Gull Service Station.
A staff member at a neighbouring premises told the Rotorua Daily Post police tape was surrounding the business.
A St John spokeswoman said a patient had been taken to hospital in a critical condition.
She said two ambulances, one helicopter, one response vehicle and an operations manager were sent to the scene.
