55 arrests in police blitz

North Shore police have made 55 arrests in a four-day operation targeting known offenders.

Operation Hammer involved checkpoints, mobile patrols and high visibility policing.

Police tactics co-ordinator Senior Sergeant Gary Hill said the suburbs included Northcote, Glenfield, Birkdale, Beach Haven and Wairau Valley.

"The whole idea of the operation was to make it known to our repeat offenders that we haven't forgotten about them, and that we will take action if they step out of line."