Handcuffs, handheld radios and a police-style tactical belt were among several items found inside the home of a man claiming to be an "authorised officer".

An Auckland man was driving home about 11.50pm on January 24 when he was followed into a parking building by a man driving a BMW motorcycle with flashing lights.

The motorcyclist, later identified as 24-year-old Shannen​ Cox, was dressed in black and had a GoPro on his helmet. Cox told the man he was an authorised officer and had the power to stop him and question him about his behaviour. Cox then showed the victim a Land Transport badge.

There have not been separate Ministry of Transport traffic officers in New Zealand since they merged with police in 1992.

The victim, Richard, who did not want his last name published, began to record the conversation and called police. Cox then left the scene.

Police arrested Cox at his home three days later. They found handcuffs with a key, an extendable ASP baton, handheld radios, a police-style tactical belt and traffic controller and Fulton Hogan identification cards inside Cox's house.

Cox declined to comment when initially spoken to by police.

He later pleaded guilty in the Waitakere District Court to impersonating police. He is due to be sentenced next month.

Cox declined to comment when approached on Tuesday.

"Get lost ... go away or I will phone the police," he said.

Richard told Stuff Cox was "quite persuasive" and he worried other people may have been pulled over by him.

"I was able to figure out what was going on, most people probably wouldn't have."

He said he was confused when he saw the flashing lights behind him as he entered the garage.

"I just thought 'oh my god, why are the police coming into the building? It must be something significant'.

"It was a bit of a shock to the system at that time of night. I was wondering what have I done wrong and what's going on here?"

Cox looked the part until he said he would show his Land Transport badge.

"The bike was the right type, the vest he was wearing, the little torch and the radio looked like police, but the ID said LTSA – I thought about that and I didn't think it seemed right."

A police spokeswoman said while instances of people pretending to be police officers were rare, they were taken "extremely seriously" by police.

"Anyone committing this offence can be liable for a maximum term of imprisonment of 12 months and a fine of $15,000.

"Police encourage anyone with concerns to request to see official police identification, or they can contact 111 to check the person is who they say they are."

Police ordered the items found at Cox's home be destroyed.

Cox previously came to police attention after he allegedly impersonated a medic at a Christchurch rugby game.

He said at the time he was at the game as a spectator, saw a player suffer what he believed to be a serious neck injury in a tackle, and grabbed his first aid kit from the back of his car. Although he was not employed in any medical work, he said he "just happened to be at the right place at the right time".