Rogue traders are reportedly overcharging people for asphalting driveways.
Police say labourers, led by young Englishmen, have been door-knocking and offering to seal driveways in Auckland and Wellington.
Some customers have paid up to $20,000 for the work and have no option for redress.
Detective Senior Sergeant Dave Thornton says they're doing a quick job at a high price.
He says they are well-presented, with a smooth sales pitch and are doing their deals in cash.
He says they may have moved to Christchurch and police are keen to find them before they leave New Zealand.