Speeding Auckland motorists be warned, police have a new tool in their fight against dangerous drivers in the Super City - an unmarked motorbike.

The motorcycle has recently arrived in Auckland, part of a national trial that began in Canterbury in March then moved to Wellington.

The blue Yamaha MT09TRAP 900cc, resembling a large touring bike, has recently been spotted by eagle-eyed Auckland motorists on city highways.

It has red and blue flashing lights and is ridden by an officer in plain motorcycle gear, rather than the motorbike uniforms with insignia worn by other riders in police bike squads.

The unmarked motorcycle is now being used across Auckland, a police spokeswoman said.

A second unmarked motorcycle is set to roll out next month for deployment in additional districts outside Auckland, she said.

"The trial will continue through until early next year with the motorcycles rotating through districts.

"The motorcycle riders have been issued with a plainclothes uniform but still have their marked operational uniform which they will use if operational need requires it."

In a statement announcing the Canterbury leg of the trial, National Road Policing Centre director Superintendent Steve Greally said that this initiative was aimed at unsafe behaviour, including failing to wear a set belt and using cellphones.

"The fact that these motorcycles will not be immediately obvious as police vehicles, is expected to have a positive impact in death and serious injuries as it has overseas jurisdictions," he said.

Senior Constable Mark Middleton, of the Christchurch police motorcycle squad, said at the time the unmarked bike had received a positive reception.

"I've completed three shifts with the bike, and I've stopped and chatted with at least 100 motorists. The reaction so far has been absolutely positive.

"No one has expressed any doubt as to my role, the red and blue flashing lights are particularly visible at night and are accepted without question."