According to Const. Manuel Couture of Montreal police, two officers found injured men on the sidewalk while out patrolling the busy nightlife area at closing time.
Couture said the men were in different spots but all relatively close to each other.
Two men appear to have been shot while two others were stabbed. Montreal police later confirmed it was two groups of two who fought.
All four were transported to hospital. One of the young men is in stable condition, while the other three sustained life-threatening injuries.
Police are still investigating the events that led to the violent altercation.
St-Laurent Boulevard was closed between Sherbrooke and Roy streets for the majority of the day.