An Australian woman who was about to get married was fatally shot overnight Saturday by a Minneapolis police officer who did not have his body cameras turned on, officials said.

The woman, Justine Damond, was shot as the officers were responding to her 911 call of an assault near her home in the Fulton neighborhood. Ms. Damond, 40, who is from Sydney and who also went by the name Justine Ruszczyk, was engaged to be married next month to an American man, according to Australian news media reports.

Police officials said they were looking into the circumstances of the shooting, and why the officers were not using their body cameras, as required in such encounters.

“Two Minneapolis police officers responded to a 911 call of a possible assault just north of the 5100 block of Washburn Avenue South just before 11:30 p.m. Saturday,” a statement by the State Bureau of Criminal Apprehension said. “At one point an officer fired their weapon, fatally striking a woman.”

“The officers’ body cameras were not turned on at the time and the squad camera did not capture the incident,” the statement added.

Betsy Hodges, the mayor of Minneapolis, said she was “deeply disturbed” by the killing.

“As mayor of our city, a wife, and a grandmother, I am heartsick and deeply disturbed by what occurred last night,” she posted on Facebook.

Ms. Damond’s website said she was trained as a veterinarian and was now working as a spiritual healer and meditation coach.

“Her interest in supporting people to heal and transform themselves developed after she saw family members suffer greatly from depression, alcoholism and cancer,” her website said. “After losing much of her family to cancer she has spent many years on a personal investigative journey to discover how habits and disease develop, and how people can change and live in joy, expressing their full potential.”

The website said she had recently relocated to Minneapolis. The Sydney Morning Herald said that she was engaged to be married to Don Damond, a businessman, in August.

Residents of the upscale neighborhood held a vigil on Sunday night for the family, and Mr. Damond and his son Zach attended.

“Basically my mom’s dead because a police officer shot her for reasons I don’t know,” he told The Star Tribune of Minneapolis. “I demand answers. If anybody can help, just call police and demand answers. I’m so done with all this violence.”

Minneapolis police officers began wearing body cameras last summer and are now required to use them when responding to “critical incidents.” A critical incident is defined as “the use of deadly force by or against a Minneapolis police officer” or “death or great bodily harm to a person who is in the custody or control of an officer.”

“They are not the final step in transparency, but they are a big step toward it,” the city government said in a statement announcing the change. The requirement came as the Twin Cities area was shaken by the police killing last summer of Philando Castile, a black driver whose girlfriend live-streamed the aftermath of the encounter outside St. Paul.

Ms. Damond conducted meditation workshops at the Lake Harriet Spiritual Community, which posted a tribute to her on its Facebook page.

“We are so sad to report the tragic shooting of Justine Damond,” the post said. “Justine was one of the most loving people you would ever meet. We can’t even imagine LHSC with out her.”

Matt Omo, a close friend in Australia and a founder of his own wellness practice who often collaborated with Ms. Damond on meditation and personal development workshops, called her death a horrible tragedy.

“How could such a beautiful soul,” he asked, “with only the desire to help people be shot dead by the police?” he wrote in a Facebook message.

Mr. Omo, who is from Indiana, said Ms. Damond moved to the United States about three years ago because her fiancé could not move to Australia with his son and work.

“They were so in love,” Mr. Omo said.