Ontario's Special Investigations Unit (SIU) is investigating the circumstances surrounding the death of a 33-year-old man following his arrest in the city's west end on Saturday.

Around 12:30 p.m., Toronto police officers responded to an Etobicoke residence in the area of Burlington Street and Victoria Street to assist Emergency Medical Services, the SIU wrote in a press release.

Upon arrival, officers arrested the man, but "soon after, he went vital signs absent," the police watchdog said.

The man was taken to hospital where he was pronounced dead.

The SIU is an independent agency that investigates incidents involving police where someone is sexually assaulted, injured or killed.

Two SIU investigators and one forensic investigator have been assigned to the incident, and the unit is urging anyone who may have information to contact the lead investigator at 1-800-787-8529.

Anyone with video evidence related to the incident is asked to upload that video through the SIU website.