The SIU has invoked its mandate after an early morning collision on McCaul Street, north of Dundas.
Police have not released information, but reportedly it happened after midnight on Wednesday, during a high speed chase.
A vehicle rolled-over in a small parking lot in the area.
There are reports from the scene that one person was taken into custody, but that hasn't been confirmed.
The Special Investigations Unit is called in whenever police officers are involved in incidents where someone has been seriously injured, dies or alleges sexual assault.