Police are getting help from the New Zealand Transport Association after today's drug busts on Headhunters gang properties in the upper North Island.

Properties in West Auckland, Tauranga and Huntly are among those raided by police.

Detective Inspector Bruce Good said documents were discovered at some of the addresses suggesting car and motorcycle licenses were fraudulently issued to some gang members.

Three testing agencies certified by NZTA are being investigated.

Detective Inspector Good said they don't know just how many licenses were issued and it will be an on-going investigation alongside the drug-related arrests already made.