Power retailers had also been informed that impostors were trying to get into people's homes by posing as subcontractors, Mr Worsfold said.
"Always ask for identification, and if you are suspicious of anything, please ring the police."
A spokeswoman for Kerikeri police advised people to ask for ID before allowing anyone claiming to be from a power company into their home, especially if they weren't wearing a uniform and had an unmarked car.
Another strategy was to ask for their company's phone number, make them wait outside, and call their office to check they were genuine before allowing them in. If they could not produce ID or a genuine phone number they were impostors. If they then refused to leave it was time to call 111.
To make a complaint about fake power company workers call Kerikeri police on (09) 407 9211, Kaikohe on (09) 405 2960 and Kaitaia on (09) 408 6500.