Ontario's police watchdog is investigating the death of a man who went into medical distress after he was involved in a fight and then taken into custody outside a downtown Toronto strip club early Thursday morning.

The Special Investigations Unit is describing it as a "police-involved custody death."

Police officers were called to the fight involving two men at Remington's Men of Steel on Yonge Street, south of Gerrard Street, around 1:30 a.m. Initially, there was a report that a man was trying to pick fights with people inside the male strip club.

When officers arrived, they separated the men and placed them in separate police cruisers, but one of the men soon went into medical distress as police investigated the fight, CP24's Cam Woolley reported.

Police had already requested an ambulance because of injuries suffered in the fight. They ordered a rush on the ambulance when the man went into medical distress.

The man, described by the SIU as a strip club patron, was without vital signs when he was rushed to a trauma centre. He was later pronounced dead.

Police have not released any information because the SIU has invoked its mandate, but they continue to investigate the circumstances of the fight.

Forensic investigators from the SIU and Toronto police were at the scene to collect evidence Thursday morning.

The SIU is involved because it is the provincial agency that investigates reports involving police where there has been a death, serious injury or allegations of sexual assault.

The SIU has assigned five investigators and two forensic investigators to the case.

With files from CP24 reporter Cam Woolley.