An Auckland police officer swore, called a man a c***, made racist remarks and threatened to use pepper spray on a man during an arrest last year, the Independent Police Conduct Authority has found.

Police officers spiked a car speeding along St Lukes Rd in Auckland on March 4 last year and told the occupants to get out of the car and on to the ground.

One of the occupants of the car said they did what they were told, but later complained an officer assaulted him during the arrest.

The man told the IPCA he had been asleep in the back of the car, but woke up when the car was spiked. He claimed he did not resist arrest, but felt police officers slam him on the ground "like a dog".

He said an officer told him to: "Stop fucking resisting you little c***".

Other officers arrived and helped their colleagues restrain the man who they told the IPCA was "thrashing around".

A number of officers interviewed by the IPCA said the man was resisting arrest and Police Eagle footage also backed this up.

The man said officers told him to "shut up" when he was struggling to breathe. He felt a kick to his forehead when he turned his head to check on a friend and was left with a graze on his face.

He was handcuffed and taken back to the police car when he said one of the officers told him to, "f*** off back to whatever island you came from".

The man said he told the police officer he had been thinking about joining the police force until his treatment, to which the officer replied: "We don't want you c***".

The officer at the centre of the allegations left the police force shortly after the incident and declined to be interviewed by the IPCA.

But another officer who was in attendance said the officer was "verbally provoking and baiting" the man. At one point she had to stand between the man and the officer to stop them squaring off.

She also heard the officer threaten to use the pepper spray on the man if he did not get off the ground, while holding it to his head.

The IPCA ruled that the officer acted unprofessionally towards the man during the arrest by inappropriately threatening to use pepper spray, and using offensive and derogatory language towards him.

"Officer E failed to act in a manner that would be reasonably expected of an experienced, well-trained police officer."

It could not determine whether the kick to the head was deliberate or accidental and who was responsible for it.

In a statement today, Auckland City District Commander Superintendent Karyn Malthus acknowledged the IPCA's findings and said using offensive or derogatory language was completely unacceptable and not in line with police values.

"We would note that the officer left police completely unrelated to this complaint after having served the community for a significant number of years and was not interviewed as part of this process."