A police officer's careless driving has been blamed for injuries to a motorcyclist during a pursuit in Christchurch.
The Independent Police Conduct Authority has released its findings on the 30 August 2017 pursuit.
The chase began about 3.15am in Waltham when two officers saw a motorcyclist drive past in a "dangerous manner" with no lights and not wearing a helmet.
The police car was going about twice the speed of the motorbike when they collided on a corner, causing the rider to hit a concrete footpath and break his ankle.
The Independent Police Conduct Authority (IPCA) said the officer who was driving should have abandoned the pursuit when the motorcyclist didn't stop.
Authority chair Judge Colin Doherty said the officer's manner of driving was "at the very least, careless".
"The officer did not drive in accordance with best practice for a pursuit, as he was following the motorcycle too closely, and was not aware of the speed at which the police car or motorcycle were travelling."
The authority also found the officers were not justified in presenting guns as they approached the rider after the crash, and in failing to advise their communications centre they were equipping themselves with firearms.
Acting District Commander Superintendent Mike Johnson said in a statement the decision to pursue a fleeing driver was one of the most complex and difficult decisions police officers had to make, but he accepted the findings.
"While police manage fleeing driver events well, there is room for improvement especially around risk assessments," he said.
Police said they were considering what action to take in relation to the officers.