Police have found no evidence Google committed a criminal offence by gathering personal wireless internet data during its street view operation in New Zealand.

They have referred the matter back to the Privacy Commissioner.

The commission in June asked police to investigate a possible breach of the Crimes Act after concerns were raised that Google had collected unencrypted Wi-Fi data while photographing streets with 3D cameras for its street view mapping service.

Google has admitted collecting public Wi-Fi data in more than 30 countries, though it was not known what kind of information had been collected. The company "locked-down" the information while the matter was being investigated.

Detective Senior Sergeant John van den Heuvel, of the police national cyber crime centre, said there was no evidence to suggest Google had committed a criminal offence.

The matter was a timely reminder about Wi-Fi security, he said.

"Anyone using Wi-Fi needs to ensure they have appropriate security measures in place.

"People should not underestimate the risk that information they broadcast might be accessed by others, either inadvertently or for more sinister purposes."