Ontario's police watchdog is investigating the death of a man at the VELD music festival early Monday at Downsview Park. 

The Special Investigations Unit says a police officer who was working at the concert went to help two people who were seen carrying a man.

But when the officer called for an ambulance, the SIU says the man became violent and needed to be handcuffed.

Paramedics say he died suddenly on the way to hospital. SIU investigates any incident in which someone suffers serious injury or death during an interaction with police.