Police says motorbike riders must take care, after four crashes at an organised police, monitored event on Saturday - between Whatawhata North and Huntly

At 11am a woman skidded on gravel on Te Pahu Road fracturing her wrist - and a man who came off 10 minutes later on the same road, was knocked out.

After midday, a rider broke his arm in a crash on Arapuni Road - and another came off riding two abreast.

Superintendent Steve Greally says the consequences of mistakes on a motorbike can be far worse than for other vehicles.