Police have confirmed a scene examination is underway at CityLife Hotel in Auckland Central, where Grace Millane was last seen on Saturday evening with a male companion.
After going through hours of CCTV footage, police say the last known sighting of Ms Millane, a British backpacker, was at the entry to the hotel at 9:41pm on Saturday night.
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The male companion Ms Millane was with has been identified and spoken to police but no further details were provided. He is not in custody.
An investigation into the connection between Ms Millane and the man was underway, while an apartment at the hotel has been identified as a location of interest.
It is unknown if Ms Millane left the CityLife Hotel.
After being missing since Saturday, Det Insp Scott Beard said police hold "grave fears for her safety", but have "no evidence of foul play" at the moment.
It is believed Ms Millane had two cellphones, one English and one New Zealand, but Det Insp Beard said there could be more.
Ms Millane's father, David, arrived in New Zealand from England on Friday morning and addressed media at the Auckland Central police station in the afternoon visibly distressed.
"Grace is a loving, out-going, fun-loving, family orientated daughter," he said while fighting back tears.
He said she had never been out of contact for such a length of time.
"We are all extremely upset and it is very difficult at this time to describe the range of emotions we are going through," he said.
Ms Millane began a one year overseas experience in late October, travelling to South America before arriving in New Zealand on November 20.
Up until her disappearance, Mr Millane said his daughter had been bombarding her family with photographs.
He asked that their privacy was respected and appealed for even the smallest amount of information about Ms Millane's whereabouts.