The province's police watchdog has been called in after a standoff in Toronto turned deadly.

The incident began shortly after noon on Wednesday at a low-rise apartment, on Sherbourne Street near Wellesley Street, in the city's downtown east-end where police believed a man was armed with a gun.

The Special Investigations Unit says officers spoke with the man, and shortly after that the police emergency task force was called in.

It says that just before 2 p.m. a gun was fired and the man fatally struck — but the circumstances of the fatal shot aren't clear.

The incident sent a nearby elementary school into lockdown as a precautionary measure, and the Toronto Catholic District School Board says the students were safe.

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.