The 26-year-old who has been speaking with police about the disappearance of Grace Millane will be charged with her murder.
He will remain in police custody until Monday morning when he will appear in the Auckland District Court.
The 26-year-old is the same man who was questioned previously by police and was with Ms Millane at several places, including Sky City, before going to CityLife Hotel with her.
The Millane family have requested privacy at this time and will not be making any further statements at this stage.
Detective Inspector Scott Beard briefed media in Auckland earlier this afternoon and said they were treating her disappearance as a homicide.
"The evidence we have located so far, our scene examination, some of the CCTV footage we have, and our investigation has determined that Grace is no longer alive and this is a murder investigation.
"A 26-year-old man was located at a central Auckland address by police. He was brought back here to Auckland Central Police Station and is currently speaking to us in relation to the murder of Grace Millane.
"Grace's family have been advised of this development and they are devastated."
"We still do not know where Grace is. We are determined to find her and return her to her family," Mr Beard said.
"We have no understanding of what the motive was."
Police have identified and secured a vehicle of interest.
Mr Beard said Ms Millane's passport, necklace and watch were still missing and police wanted anyone with information on these or anything else to get in touch on 0800 676 255.
"Everybody who is a parent out there will understand what their family is going through.
"There's family back in the UK and our hearts go out to them as well."
Detectives said yesterday they were continuing to view hundreds of hours of CCTV footage, while they continue to examine the CityLife Hotel in central Auckland, where she was last seen entering with a man on Saturday night.
More than 25 Police staff are now working on the investigation into the disappearance.
Her father, David Millane, has travelled to New Zealand and held an emotional press conference yesterday.
Mr Millane struggled to hold in his emotions as he told media yesterday of his worry for his daughter.
"Grace is a lovely, outgoing, fun loving, family orientated daughter."
'We thought maybe it's just the time zone'
Ms Millane left the UK six weeks ago to travel the world after finishing university.
Her brother, Michael Millane, said the family began getting worried on Monday when she did not reply to messages.
"We sort of noticed Gracie hadn't really texted back or hadn't read anything, which was obviously really strange because it was her birthday.
"We thought maybe it's just the time zone, sort of catching up, but we looked into it and realised her messages hadn't been read or delivered."
Social media platforms have been flooded with messages of support for the family of the murdered backpacker.
On Instagram, Ms Millane's final post has been inundated with comments expressing sadness and heartbreak at her death.