The woman shot and killed by a Calgary police officer on Wednesday morning had pepper sprayed and scuffled with the female officer who responded to the call, Calgary Police said during a press conference.

Around 6:30 a.m., the officer was responding to a call of a "suspicious person wandering in and out of several backyards" in the area of 20th Avenue and 35th Street S.E., said Acting Deputy Chief Steve Barlow.

"The officer encountered a woman in her 30s who first pepper sprayed her. A physical altercation then took place between the two, ending with the woman being shot."

The woman later died in hospital.

A witness who was dropping off his son around 6:45 on Wednesday said he saw the officer and the woman talking, and then struggling in the alley, and saw that the woman was on the officer's back.

"They were both talking very casually. I dropped my son off, it takes 10 seconds. I come out and they're not there anymore, and I look down the alleyway there and that's where the struggle was happening," said the man, who was granted confidentiality due to concerns for his safety and the safety of his family.

"There was shouting, she was like, 'get your hands off my gun, hands off my gun.' And then she spun around and the offender kept coming at her and she shot twice."

The man said the woman who was shot did not go down after the first shot, but fell after the second.

Name not released

Barlow said police have identified the woman but her name will not be released, and that next of kin had not yet been notified. Barlow confirmed that the woman was known to police.

"This morning's incident highlights this reality that there are no routine calls," Barlow said, of the seemingly mundane nature of the initial call. "We have over 35,000 calls like this a year when it comes to suspicious persons, and some of them will unfold very, very quickly as this one did today, and end up in a horrible situation."

The officer, who has been on the force for six years, was treated on the scene for minor injuries.

"I can only commend her on how she handled this situation, it's a horrible outcome," Barlow said. "No officer ever comes to work in a day and wants to, or is planning to be, in a situation like this."

The officer has been placed on administrative leave for 30 days.

Calgary police at the scene where an officer shot a woman on Wednesday. (Mike Symington/CBC)

The incident took place behind Cally Berry's home, but she says she was sleeping at the time and didn't hear anything.

"We've experienced break-ins, like into our vehicles. We've had somebody break into our garage before. We can't leave stuff in our backyard just because people will root through them," she said.

"It's unfortunate and really sad, but weird things happen around here all the time."

Berry said that for something like this to happen so close to home "doesn't make you feel very good about hanging out outside."