Adern choked back tears as she described the collective feeling of shame in the South Pacific nation over the murder of Millane, whose body was found dumped in parkland near Auckland on Sunday.
"I cannot imagine the grief of her family and what they will be experiencing and feeling right now,” Ardern said during a post-cabinet address in Wellington.
"My thoughts and prayers are with her father, David who is in the country, her mother who cannot be here and her wider family, friends and loved ones."
"From the Kiwis I have spoken to, there is this overwhelming sense of hurt and shame that this has happened in our country, a place that prides itself on our hospitality on our manakitanga [kindness, generosity, support and respect], especially to those who are visiting our shores.”
"So on behalf of New Zealand, I want to apologise to Grace's family - your daughter should have been safe here and she wasn't, and I'm sorry for that."
Described by her father David as fun-loving and family-oriented, Grace had been traveling in New Zealand as part of a yearlong trip away. She went missing on December 1, on the eve of her 22nd birthday, and her family’s worst fears were confirmed when her body was found a week later.
Detective Inspector Scott Beard said she met a man for a couple of hours in the evening before surveillance cameras showed them entering the CityLife hotel around 9.40pm.
A 26-year-old man, who cannot be named for legal reasons, faced Auckland District Court on Monday charged with her murder.