"Initially, properties on the Thames Coast Rd, north of Thames, and further south towards Ngatea were affected, with thieves cashing in cheques to the value of about $12,500 at a time. But since then, speaking to colleagues in other districts we have identified victims from around Auckland, Taupo, Palmerston North and Canterbury."
So far 16 victims had been identified who had lost about $100,000.
Police and banks have identified two people of interest through CCTV footage.
"Police urge rural residents to report suspicious behaviour, particularly around rural mailboxes, and if you have the opportunity, take down registration numbers and descriptions of people," Mr McDonald said.
They are advised to pay their bills electronically instead of by post.
Anyone with information is asked to contact Detective Rachel Holmes on (07) 867 9621.