A Texas police officer shot and killed a woman when he fired repeatedly at a dog that was running at him, authorities said.

The officer was among those responding to a welfare check for 30-year-old Margarita Victoria Brooks who appeared to be unconscious on grass near to a shopping centre in Arlington.

Footage from the officer's body-worn camera released on Friday shows the officer walking along a sidewalk and calling out "Hello. Are you OK?"

The woman replies, "Yeah, I'm fine." A dog approaches and the officer asks, "Is that your dog?"

Margarita Victoria Brooks who was shot dead by police. (Facebook)

As the barking dog runs toward him, the officer yells, "Get back!" He begins to back up and then fires three shots. The woman screams, "Oh, my God!" and continues to cry out.

Police Chief Will Johnson said the dog, which he described as a Labrador mix, weighed about 40 pounds (18kg) and investigators believe it belonged to the deceased woman.

Ms Brooks was shot in the "upper torso," Mr Johnson said, while the dog suffered a flesh wound and has been quarantined.

He added: "Everything about this call is an absolute tragedy.

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"Our hearts are broken for the Brooks family and for the officer involved. Our officer was on scene trying to find an individual who may be suffering from a medical emergency.

"Clearly, this is not the outcome the officer wanted, nor is it the outcome that the department wanted."

The 25-year-old officer, whose name has not been released, graduated from the police academy in February and had not fired his service weapon in the line of duty before the incident on Thursday, Mr Johnson said.

He has been placed on administrative leave.