On the New Zealand Police Conduct Association website it reported the matter was historic as the woman had always been too scared to speak out until now.
She had filed a formal complaint with the Independent Police Conduct Authority.
Inspector Donna Laban, Senior Police Professional Conduct Manager based at police headquarters in Wellington, said in a written response to questions by the Northern Advocate police were aware a complaint had been received by the Independent Police Conduct Authority last week in relation to the matter.
"There is now a formal process that will need to be completed by the IPCA and police," Ms Laban said.
"We are unable to make any further comment at this stage."
Police would not comment on when or where the alleged incident happened, or if the officer was continuing to work while there was an investigation under way. It's believed the officer is still working in the Northland police district.
The IPCA confirmed it had received a complaint and preliminary investigations had been launched.
The IPCA is an independent body that considers complaints against the New Zealand Police and oversees their conduct.
The Authority's functions are to receive complaints about police employees, practice, policy, or procedure and investigate those complaints and make recommendations based on their investigations.
The IPCA website says when the Authority receives a complaint, it may carry out its own investigation, or refer the matter to the police for investigation under the Authority's oversight.
If a complaint is referred to the police for investigation, the Authority will take steps to ensure that it is properly resolved.
This may include directing or actively overseeing the police investigation, or reviewing or auditing the police investigation once it is completed.