Three police officers are facing charges over allegations of assaults done on duty, including one "renegade" cop accused of attacks on five people in as many months.

The alleged attacks took place between October last year and January this year in Auckland's Waitemata policing district.

One alleged victim has called for an inquiry into police brutality after being injured so badly in a police station cell he lost a testicle.

Police Minister Judith Collins said last night she had been briefed on the charges faced by the three officers and dismissed the call for an inquiry.

"I don't believe there is a culture of violence in [Waitemata] police or among police anywhere else in the country."

A Police National Headquarters spokesman said no comment would be made on the case or accusations of police brutality. He said it was "not an urgent thing".

Waitemata District Commander Superintendent Bill Searle also refused to discuss the case, or comment on whether there was a culture of violence in his ranks.

One officer appeared in North Shore District Court on Friday facing four charges of common assault between October and December and one of assault with intent to injure in January.

He was remanded on bail until his next court date and given name suppression, protecting his rank and the station he worked at.

The officer refused to speak to the Herald on Sunday. A supporter told the newspaper outside court: "Your sources that tell you things better watch out."

It is understood police bosses launched a criminal investigation after some of the officer's colleagues approached them, concerned about his actions.

Two other officers were investigated and will appear in court this week on charges relating to at least one of the assaults. All three officers have been stood down from duty.

One of the alleged victims - who also has name suppression - revealed he did not press charges against the officer who appeared in court and has little memory of the alleged assault.

The man was arrested for being disorderly on January 8 after being involved in an altercation that he said left him concussed and confused.

He spent the night at a police station in the Waitemata district and was released the next day with little memory of what happened. His injured testicle had to be removed surgically.

The man said he believed the group he fought with had caused the injury until he was contacted by a detective.

"I was really surprised. She rang and I asked if I was in trouble. She said ... as a result of going through CCTV footage of me in the cells, she discovered I had been seriously injured by police while in custody."

He said the detective told him there were five officers in the cell during the alleged assault. He said he was told the footage showed he was in handcuffs.

He said he did not want to press charges and having the officer stood down from work would be enough. But he wanted a full inquiry.

"If something had been done earlier it wouldn't have happened. If they had cottoned on earlier, what happened to me wouldn't have happened.

"Police are no different from the likes of you and me. Laws are in place and we've all got to follow them - even they have to."

A police source said the accused officer was "a good street cop ... but he's what you'd call high maintenance ... in the past it's been nothing but trouble".

"He's always had a bit of a shadow around him, being a bit of a renegade, a bit stroppy."

The source commended the officer's colleagues for approaching management. "About three or four cops came forward and said 'this is what he's done'. That's a big deal.

"It's got to be really significant for cops to come forward and break the old blue wall of silence.

"Years ago no one would say anything."

The Police Association would not say if they were supporting the officer or helping him with legal representation.

An Independent Police Complaints Authority inquiry is in its early stages.

A string of assault cases have dogged police in recent years. In March a High Court judge found Whakatane police subjected Rawiri Falwasser to an excessive abuse of power over seven hours in a cell.

He was repeatedly squirted with pepper spray and hit with a baton.

In 2003 South Auckland police officer Alexander Grant was sentenced to 16 months in prison after he assaulted a handcuffed man in the back of patrol car.