Hamilton police have taken the unusual step of arresting the passenger in a boy racer car.

The man is being charged with aiding reckless driving after police allege he egged on the driver of a car spotted doing donuts in the city in the early hours of this morning, navigated for him and encouraged him to flee from police. The chase took place in heavy rain at excessive speeds.

The driver eventually stopped just north of Ngaruawahia and told officers he was from Auckland and had to rely on his passenger's local knowledge for directions.

The driver also faces charges.