Nine-year-old Jasmine Olleik is still missing as of Sunday afternoon and is believed to be with her mother, who does not have custody rights, police say.
Her mother lives in Toronto, according to Ottawa police.
Toronto police have been notified.
Olleik was last seen on Wednesday at about 3 p.m. She was walking with a woman and was seen getting into a blue, four-door sedan in the 1500-block of Blohm Drive in Ottawa's south end.
The girl was wearing a pink winter jacket and pink and brown boots that day.
Her father, who has full custody, reported her missing later that day. He told police he believed the girl's mother, 42-year-old Nina Grebenschikov, had likely taken the girl.
An Amber Alert was not issued. Cases of missing children have to meet a strict set of criteria for an alert to be issued. They're typically issued when children are believed to be with strangers, or if foul play is believed to be involved.
Olleik is described as a white girl standing at five feet one inch tall with a slim build, short, dark brown hair and brown eyes.
Her mother is a white woman, standing about five feet seven inches tall and weighing about 125 pounds. She has auburn hair and hazel eyes, but might have recently dyed her hair blonde, police said.
Anyone with information is asked to contact the Ottawa police partner assault unit at 613-236-1222, ext. 5407, or Crime Stoppers at 613-233-8477 (TIPS).