TORONTO -- Ontario's police watchdog says there will be no charges after a man was shot three times and struck with a stun gun in Toronto in December 2015.

The Special Investigations Unit says police were acting in self-defence in the incident, which sent him to hospital where he underwent surgery and survived.

The agency says police were responding to a call about a man who staff at a hospital believed had driven home drunk, when officers knocked on the man's door, and -- through the screen door -- the man warned them not to come in or there "would be trouble."

The unit says officers told the man they were there to ensure his well-being, and the man walked out of the house brandishing a 17-centimetre serrated knife.

It says officers demanded the man drop the knife, but he did not.

The SIU says one of the officers then shot the man three times, and the man remained on his feet.

The agency says a sergeant arrived and struck the man with a stun gun, who then dropped to the ground.

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.