MISSISSAUGA, Ont. -- Two Toronto police officers who shot a mentally unstable woman armed with a meat cleaver several times after she threatened to harm her young son and paramedics last November won't be facing charges.

Ontario's police watchdog agency says several people, including the 45-year-old woman, had called 911, and paramedics who responded left after the woman ran at them brandishing the knife.

The Special Investigations Unit says two officers arrived and the woman ignored several demands that she drop the knife over a period of about a minute before she rushed at them.

Unknown to the two officers, another officer with a Taser had positioned himself behind them and he deployed his weapon around the same time as the officers fired their guns, injuring her in the abdomen, pelvis and right arm.

The SIU says the young boy did not witness the shooting as he had left the house through another exit during the standoff.

Acting SIU director Joseph Martino says the evidence "reasonably establishes" that the shooting and the conducted energy weapon discharge fell within the definition of self-defence under the Criminal Code.

"While the woman was clearly not of sound mind at the time on the day in question, she clearly represented a real and present danger to herself and others," Martino said Wednesday in a release.

Martino noted that the woman recognized her faltering capacities and attempted to seek help for herself and protection for those around her when she called 911 and asked for an ambulance.

"Regrettably, by the time of the paramedics' arrival, her mental condition had taken a turn for the worse and she attacked the very people who were there to help her," he said.

The SIU is an arm's length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.