Christchurch police and the family of missing woman Tisha Lowry are fearing the worst after no word from her for seven days.
Detective Senior Sergeant Virginia Le Bas said foul play had to be considered in the case of Ms Lowry.
Ms Lowry's mother, Tanya Lowry said it was uncharacteristic for her daughter not to have been in touch for so long.
Ms Lowry, 28, was last seen by a family member about midday last Thursday in the Hampshire Street area where she was living with her grandfather, reportedly to have some time out from her 48-year-old boyfriend.
Ms Le Bas did not confirm whether Ms Lowry was living with her grandfather to seek space from her boyfriend but it was "to be in a different location and to have a little bit of space".
Ms Lowry went missing after visiting the Bower Tavern on the corner of New Brighton Road and Bower Ave with her grandfather, before walking home.
She had left her personal belongings at home, including her cellphone and handbag.
Her mother said police were unable to track her through banking transactions because her daughter did not have a bank account and her sickness benefit was paid into her boyfriend's account.
Ms Le Bas said police had been speaking to Ms Lowry's friends and family and were canvassing the area around the Bower Tavern trying to "get clues".
"I think the fact no-one has heard from her, it's unusual, does make you think something odd has gone on. It is logical that we obviously have grave concerns for her safety."
Ms Lowry's disappearance comes just a few months after Christchurch schoolgirl Marie Davis, 15, disappeared and her body was found in a river near Christchurch. Dean Stewart Cameron, 38, is charged with her rape and murder.
Last November, 20-year-old deaf woman Emma Agnew went missing and her body was found concealed in scrub north of Christchurch.
Liam James Reid is to stand trial next week for Miss Agnew's rape and murder.
