Four people have been injured in a stabbing at a shopping mall, the Arndale Centre in Manchester, police have said.
A man, 41, is being held on suspicion of terror offences after three people were stabbed and two others were hurt.
Counter-terrorism police are leading an investigation.
Police initially reported five people injured but later reduced the number. Two women and a man were hospitalised.
The centre was evacuated after the attack, during which police said a man with a large knife "started lunging and attacking people".
Two police community support officers (PCSOs) tried to confront the attacker before being chased.
Speaking at a press conference, Assistant Chief Constable Russ Jackson said it was a "random" and "brutal" attack.
"The man attacked people around him," he said.
"Although the injuries are nasty, we are told that, thankfully, none are life-threatening."
Exchange Square, which was previously closed, has since reopened, the force said.
In a tweet, Prime Minister Boris Johnson said: "Shocked by the incident in Manchester and my thoughts are with the injured and all those affected."
ACC Jackson said: "At 11:15 BST this morning, a man entered the Arndale shopping centre in Manchester city centre.
"He was armed with a large knife and, as he entered Exchange Court, began lunging, attacking people with the knife.
"Two unarmed police community support officers were in Exchange Court and attempted to confront the attacker.
"He then chased them with the knife as they were calling for urgent assistance."
Within five minutes armed officers detained the suspect on Market Street outside the centre, he added.
Three people were taken to hospital, a fourth self-presented with a "superficial" injury and a fifth person did not require hospital treatment, Greater Manchester Police said.
The force previously said two women, including a 19-year-old, were in a stable condition in hospital, while a man in his 50s was being treated in hospital for stab wounds.
One patient suffered "serious" injuries, North West Ambulance Service said.
A shop worker, who only gave his name as Jordan, 23, said the attack took place on the ground floor.
"A man was running around with a knife lunging at multiple people, one of which came into my store visibly shaken with a small graze.
"Soon after, security staff told all retail staff to close their doors and move the public to the back of the stores."
Freddie Holder, 22, from Market Drayton, Shropshire, said he heard "a load of screams just outside" the shop he was in.
He said a woman then came into the shop and told others "a guy just ran past the shop and tried to stab me".
He added: "I'm still kind of in shock from it, I'm shaking a little bit... all shops had been locked down just for safety.
"The police arrived extremely quickly, which was very lucky."
A police spokesperson said the force was "keeping an open mind" about the motivation for the attack.
"Given the location of the incident and its nature officers from Counter Terrorism Police North West are leading the investigation as we determine the circumstances," he said.
The Arndale Centre is located close to Manchester Arena, where 22 people died in a terror attack in May 2017 when a bomb was detonated at the end of an Ariana Grande concert.
The shopping centre was also damaged in a major IRA bomb in 1996.
More than 200 people were injured when the 1500kg device left on a lorry on Corporation Street exploded.