Police are investigating a confrontation between two groups of young people wielding knives in Nottingham city centre.
Nottinghamshire Police were called to Weekday Cross, near the Nottingham Contemporary, at 12:31 GMT on Wednesday after witnesses reported the violence.
A search of the area was carried out but the people involved had left, the force said
CCTV images were release on Saturday of people the force want to trace.
Police said no injuries were reported but onlookers told the BBC they feared for their lives.
Ch Insp Karl Thomas said: "I have seen the footage of this incident and share the same sense of revulsion that other viewers will feel.
"Detectives are investigating what happened as a matter of urgency and are working at speed to identify all the young people involved.
"Although incidents of this nature are rare, we fully understand the concern they cause in the community.
"I want to reassure everybody about just how seriously we are treating this incident."
Ch Insp Thomas said extra police had been deployed to patrol the area since the confrontation and he urged anyone with relevant information to contact the force.
Additional high-visibility reassurance patrols have been in place since the incident occurred as officers work to identify the young people involved.
Detectives have released a number of CCTV images of people they wish to trace to help them further their investigation.
If you know the people in the pictures or are the people in the pictures then contact Nottinghamshire Police immediately.