At least three people were shot dead in the bloody crime in a shopping center in Copenhagen.
The victims are a man between the ages of 40 and 50 and two young people, police chief inspector Søren Thomassen said on Monday night in the Danish capital, according to local media.
Three other people were seriously injured and in critical condition.
Thomassen did not provide any information about the possible motive.
The Danish police have not yet classified the attack in a Copenhagen shopping center as a terrorist act.
There is no evidence of this, said chief inspector Søren Thomassen on Monday according to TV2.
The police arrested a 22-year-old Dane in connection with the crime.
The suspected shooter was "basically known" to the police, said Thomassen.
He did not provide any further information on this.
Police believe the perpetrator acted alone.
"Until we are absolutely certain that the hypothesis is correct, we will conduct a wide-ranging investigation and maintain a massive operational presence in Copenhagen until we can say he was alone," Thomassen said.
The man had a gun and ammunition with him when he was arrested.
Another weapon may have been involved.
Interrogation of the perpetrator on Monday
The arrested person is to be questioned on Monday, it was said.
He will be charged with manslaughter.
But the allegation could still change.
The police initially did not want to say whether the man was a member of a rifle club and whether he legally owned the gun.
The Danish royal family called for cohesion.
Prime Minister Mette Frederiksen condemned the act as a "cruel attack".
"We were all brutally ripped out of the bright summer we had just begun," Fredriksen shared.
"It is incomprehensible.
Our beautiful and otherwise safe capital was changed in a split second.”
Emergency services cordoned off the entire island of Zealand, on which the Danish capital is located.
Several roads and highway exits were closed.
In order to have more forces available to investigate the bloody deed, soldiers took over guard duties from the police.
The authorities set up a place where eyewitnesses could give their testimony and receive psychological support.
Second attack in Copenhagen since late May
Field's is a large shopping center in the relatively new Ørestad area.
The large multi-purpose hall Royal Arena is also nearby.
A sold-out concert by British singer Harry Styles was planned there on Sunday.
The concert did not take place for security reasons and fans were asked to leave the hall calmly.
"I'm heartbroken, as are the people of Copenhagen.
I admire this city.
People are so warm and full of love,” Styles, 28, wrote on Twitter afterwards.
It is the second time in a short period of time that there has been an attack in a Scandinavian capital.
Just over a week ago, two people were killed and 21 others injured in a gay bar in Oslo.