Police have a new tool in their fight against dangerous drivers in Auckland

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

The 900cc blue Yamaha is now being used across the city, ridden by an officer in plain motorcycle gear.

It's recently been spotted by eagle-eyed Auckland motorists on city highways.

Police say the initiative is aimed at unsafe behaviour, including failing to wear a seat belt and using cellphones.

A second unmarked motorcycle is set to roll out next month.