MONTREAL--Montreal police are investigating three separate attacks that put people in hospital with serious injuries.

The first took place in the club district on Crescent St. at Rene Levesque Blvd. at 2 a.m. Friday, when one man stabbed another in the upper body.

Passersby found the victim lying on the ground and called 9-1-1. He was taken to hospital where he is expected to survive.

Police have arrested a man in his twenties and plan to question him, but at this point they are not calling him a suspect.

The second stabbing happened inside a Peel St. Bar across from Dorchester Square.

Many people got into a violent fight that ended with a 24-year-old woman being stabbed.

Everyone involved in that brawl fled on foot but police managed to track down and arrest four suspects.

The two men and two women, one of whom is a minor, are being questioned.

The woman was taken to hospital and should survive.

The final dangerous fight of the night happened at 3 am. outside a St. Laurent St. bar near Villeneuve St.

Again there was a brawl involving multiple people and it escalated when one person -- or several people -- beat a man in the head with a stick.

The victim, a man in his twenties, collapsed and when paramedics arrived they took him to hospital. He was badly beaten but will survive.

Police do not have a good description of the attackers, saying only that they fled in a vehicle.