A dog has been put down after it fatally mauled a woman inside her own home north-west of Adelaide.

The 39-year-old, known as Chrissy, was killed after being attacked by her dog Dexter on Murphy Crescent in Whyalla Stuart after 4pm yesterday.

Paramedics had tried to save her, but it was too late.

"There was two ambulances down the side of the street," neighbour Amy Heath said.

"We were all told we weren't allowed to leave our house, we weren't allowed to communicate with anyone else in the street."

The bulldog staffy cross was taken away by Whyalla City Council and euthanised.

Neighbours have told 9News Dexter had attacked Chrissy before.

Mayor Phil Stone called the attack "a big tragedy".

"I can't remember the last time something like this has happened in our city," Stone said.

"Over the years experts have said no matter how close you are to a pet, how friendly they are, any dog can have a bad day."

Government workers visited the home and Chrissy's partner today.

Support will also be made available to others affected by the horrific loss.

Police are preparing a report for the coroner and working to understand what happened.

They don't believe there was any human involvement in the attack.