A gunman killed on Sunday three people and wounded several others in a shooting at a mall in Denmark's capital, Copenhagen.

A 22-year-old Danish man was arrested after the shooting but his motives were unclear, police said. 

The shooter, who was believed to have acted alone, was known to the police "but only peripherally."

"He's not someone we particularly know," Copenhagen police chief Soren Thomassen told a news conference after the rare mass shooting, the first since February 2015.

The young man, who according to witnesses was armed with a large rifle, was arrested peacefully shortly after police arrived at the large Fields shopping mall, located between the city center and Copenhagen airport.

"There are three dead and several injured, three of them in critical condition," Thomassen confirmed.

The three dead were a man in his forties and two young people whose ages were not specified.

On social networks, people had been speculating about a racist motive, or some other motive, the head of the investigation said, "but I cannot say that we have anything which supports that at this moment."

Police however confirmed they were investigating videos posted online which claimed to show the suspect with weapons and pointing a gun at his head.

Styles devastated by news of the attack

The shooting occurred around 5:30 pm, causing panic in the mall. Many visitors were there for a concert with British singer Harry Styles at the nearby Royal Arena, which was canceled.

🚨VIDEO: Man with gun spotted at Fields shopping centre in Copenhagen Denmarkpic.twitter.com/1TVNE9wTJ2

— Breaking News (@NewsJunkieBreak) July 3, 2022

"My daughters were supposed to go see Harry Styles. They called me to say someone was shooting. They were in a restaurant when it happened," Hans Christian Stolz, a 53-year-old Swede who came to pick up his children, told AFP.

"We thought at first people were running because they had seen Harry Styles, then we understood that it was people in panic ... We ran for our lives," his daughter Cassandra said.

Styles said he was devastated by news of the attack.

"I'm heartbroken along with the people of Copenhagen. I adore this city," the singer posted on Twitter.

"I'm devastated for the victims, their families, and everyone hurting. I'm sorry we couldn't be together. Please look after each other," he added.

Suspect had tried to trick people

Witnesses quoted by the Danish media described how the suspect had tried to trick people by saying his weapon was a fake one, to get them to approach.

"He was sufficiently psychopathic to go and hunt people, but he wasn't running," one witness told DR state television.

Police had urged people in the building to wait inside for their arrival, calling on others to keep away from the area.

NEW - Copenhagen Police Chief says several people have been killed following a shooting at Field's shopping mall in the Danish capital earlier today‼️‼️

Police says "a 22-year-old Dane" had been arrested‼️☝😳🙏👇👇 pic.twitter.com/C3E9YEwVyC

— Sophia Dahl (@sophiadahl1) July 3, 2022

Other witnesses described the gunman as a man around 1.8 meters (five feet nine inches) tall carrying a hunting rifle.

Footage of the arrest shows the suspect, wearing a white jumpsuit to preserve DNA evidence, being picked up by officers.

"A safe capital changed in a split second"

"Denmark was hit by a cruel attack on Sunday night. Several were killed. Even more wounded. Innocent families shopping or eating out," Prime Minister Mette Frederiksen said in a statement.

"Our beautiful and usually so safe capital was changed in a split second," she expressed.

The Danish royal family said their "thoughts and deepest sympathy are with the victims and their relatives and all those affected by the tragedy."

In February of 2015, two people were killed and five injured in Copenhagen in a series of shootings.