Five revellers were treated for knife wounds after they were stabbed in a "major disturbance" in Leeds city centre.
Another five men were arrested after the fight near the Puro nightclub on Call Lane, which was caught on CCTV.
Trails of blood could still be seen on The Calls after the incident in the early hours of yesterday.
Blood spots were also found outside the Oracle bar at nearby Brewery Wharf.
A huge area, including parts of Call Lane and Crown Street, was cordoned off while police carried out their investigations, forcing shops and businesses to close.
All five victims were yesterday being treated at Leeds General Infirmary for knife wounds.
One person received serious injuries but his condition was not thought to be life-threatening.
Four of the victims were believed to come from the Nottingham area. The fifth was from Leeds.
It is thought some of those involved had earlier been in the Puro club.
Describing the outbreak of violence as "serious public disorder", a West Yorkshire Police spokesman said: "Police were called to an incident at 5.10am ... in The Calls area.
"CCTV picked up what appeared to be a disturbance. As a result of this disturbance five men were treated at Leeds General Infirmary for stab wounds."
The five men arrested in connection with the incident were later released on bail.
The Calls area is fashionable with drinkers and is home to many popular bars, including Oporto, Jake's Bar and Grill, Revolution and Elbow Rooms.
The incident happened just hours after thousands of music fans watched Leeds band The Pigeon Detectives perform in Millennium Square.
It also came less than two weeks after two men were injured in a serious fight near the GatecrasherSeven club in New Briggate.
One of those men needed surgery for a neck wound following the fracas on April 24.
He was thought to have been slashed by a broken bottle.
Anyone with information about the incident in The Calls is asked to ring West Yorkshire Police on 0845 60 60 606 or Crimestoppers anonymously on 0800 555 111.