Four teenagers were in custody on Sunday while police were granted special dispersal powers after a suspected stabbing attack in Cardiff city centre in which six people were injured.
Three people who suffered stab wounds remained at the University hospital of Wales, while another who suffered serious head injuries was at Llandough hospital in Penarth. Two people who suffered other injuries were discharged.
South Wales police said four youths, aged 16 and 17, remained in custody after being arrested on suspicion of violent disorder following a “large disturbance” in Queen Street at about 9.50pm on Saturday.
On Sunday, the force said officers had been given section 35 dispersal order powers to direct people or groups to leave the city centre for 24 hours “if their behaviour has, or is likely to contribute to disorder or cause harassment, alarm or distress to members of the public”.
Det Supt Esyr Jones said: “We want our local communities to be reassured that we are doing all we can to identify all those involved in Saturday’s wholly unacceptable violence and that the city centre remains a safe place to visit.
“These powers will enable officers to stop anyone they suspect is behaving in an antisocial manner, or who is visiting the area to cause any trouble, and direct them to leave.
“Patrols have been stepped up in the area and a dedicated team continues to investigate Saturday’s incident.”
Earlier on Sunday, Jones said: “This was a violent and completely unacceptable incident, which has understandably caused alarm within the local community.
“A team of 20 detectives are currently investigating the incident, trawling through vast amounts of CCTV and speaking to a number of witnesses, and I want to reassure the public that we will be relentless in identifying and arresting all those involved.
“This appears to have been an isolated incident involving local youths, all of whom can expect to find officers knocking at their doors as inquiries progress.
“We work closely with a wide range of partners to ensure that incidents of this nature are rare and the public should be assured that Cardiff remains a safe place in which to live, work and visit.”
Jones urged “any parent who suspects their child was involved in any way to come forward”.
He added: “Tackling knife crime is the responsibility of us all and any parents who have suspicions about their children being involved are not protecting them by remaining quiet.”
A stun gun was also used to detain one man who police said had obstructed officers responding to the incident. He is not believed to have been involved in the disorder.