A Stanley knife was believed to have been used in the fight in Northampton which left eight people in hospital.
Detectives are continuing to investigate the circumstances of the large disturbance in Bridge Street, Northampton, in the early hours of Friday morning.
Eight people were injured as a result of the incident, with six people receiving stab wounds.
Three people were taken to University Hospital Coventry for treatment while the other five, including two who sustained other injuries, were treated at Northampton General Hospital.
All eight victims are in a stable condition.
At this stage no arrests have been made in connection with the incident.
Det Insp Ally White from Northampton CID said: “Firstly, I would like to thank those people who we inconvenienced by the road closure on Friday morning for their support and patience, particularly local businesses.
“This is a complex investigation, with multiple victims who had travelled to Northampton for a night out and ended up being treated in hospital.
“We believe between 50 and 60 people were involved in the disorder, many of whom had travelled from London to an event at Nu Bar, and so part of our investigation is focused on speaking to as many of those people as possible.
“Tensions began to rise in Nu Bar and when that closed many of the people involved travelled to Faces where the fight broke out.
“ We would like to speak to anyone who may have been in either bar in the early hours of Friday morning – any small piece of information could help with our investigation.
“At this stage a sharp implement, possibly a Stanley knife, is believed to have been used to stab the victims, and we urge anyone who may have found a knife in the town centre to contact us on 101.”
Closed circuit television footage has been reviewed by officers investigating the incident.
Chief Insp Mark Evans, Northampton’s operations commander, added: “I would like to reassure people that we are using every available power and tool to prevent any re-occurrence of this type of incident, which is thankfully highly unusual for Northampton.
“This Thursday night we will have officers on patrol in the town centre to speak to anyone who may have been out last week and who we haven’t spoken to yet.
“We have been working with an increased number of police officers for a number of weeks as part of our festive planning and that is why we were able to respond quickly to the incident.
“I can reassure the public that this increase in numbers will also be in place this weekend as traditionally, the Friday, Saturday and Sunday before Christmas is a busy time in the town centre.
“Northampton Council’s licensing sub-committee met on Friday evening and agreed to suspend the licenses for both Nu Bar and Faces for seven days.
“We will continue to work with licensees and the licensing authority to ensure we are properly sighted on large-scale events in the town centre.
“We want everyone visiting Northampton town centre at night to have an enjoyable time, especially in the week before Christmas, and will have an increased number of officers on duty this Friday and Saturday night, to help people celebrate in peace.”
Witnesses should call the police on 101 or Crimestoppers anonymously on 0800 555 111.