Many of the victims are believed to have stayed temporarily in the main dwelling of Main Street Lodge over the past two and a half years, police said.
The business offers backpacking facilities, hotel units and, on occasion, longer term accommodation in the owner's residence.
Police are continuing to investigate the allegations, and have asked for people to come forward.
"It is very important for us to speak to anybody who has stayed in the owner's residence over the last two and a half years," Detective Senior Sergeant Rhys Johnston said.
"These victims are unlikely to know that something has happened to them, although they may have suspicions.
"We will deal sensitively with them and offer all appropriate support required.
"This is an ongoing investigation and we have a lot of work ahead to assess evidence and establish if there are further victims we are not yet aware of."
A helpline number and email address have been set up so potential victims can get in touch with the investigation team.
Anyone with information, or who believes they may have been indecently assaulted, is asked to contact 0800 762 701 or operationsnap@police.govt.nz