The gunman who opened fire in a shopping mall in the Danish capital Copenhagen most likely acted alone and selected his victims at random, the police said Monday, adding that the 22-year-old suspect in the weekend shooting that left three dead was known to mental health services.

Copenhagen police chief Soren Thomassen said investigators do not believe the previous day's attack was terror-related.

"Our suspect is also known among psychiatric services, beyond that I do not wish to comment," Thomassen told a press conference, adding that there was nothing to indicate it was an act of terror.

Thomassen also said three people were killed – two Danes and one Russian citizen – and two Danes and two Swedes are hospitalized with serious injuries.

The three dead were a man in his 40s and two young people whose ages were not specified.

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

Thomassen earlier had described the apprehended suspect, as a 22-year-old "ethnic Dane," but said it was too early to establish a motive.

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.

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.

They had no indication that the man had acted together with others, and police were maintaining an increased presence both around the shopping mall and across Copenhagen, he added.

The rare mass shooting, the first since February 2015 in the country, occured two days after this year's Tour de France cycling competition took off from Copenhagen, and the Tour organizers released a statement expressing their sympathy.

"The entire caravan of the Tour de France sends its sincerest condolences to the victims and their families," it said.

Images from the scene showed parents carrying their children as they ran from the building and ambulance personnel carrying people away on stretchers.

Eyewitnesses quoted by Danish media said they had seen more than 100 people rush towards the mall's exit as the first shots were fired.

"We could see that many people suddenly ran towards the exit and then we heard a bang," Thea Schmidt, who was in the mall at the time of the attack told broadcaster TV2. "Then we ran out of Field's too."

'We heard gunshots'

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

Police also asked witnesses to get in touch with them and called on those who had been visiting the shopping mall to contact loved ones to reassure them.

"All of a sudden we heard gunshots, I heard 10 shots, and we ran as far as we could to take refuge in the toilet," Isabella told public broadcaster DR. She said she had hidden in the mall for two hours.

Other witnesses described the gunman as a man around 1.8 meters tall (5 feet 9 inches) carrying a hunting rifle.

At around 7:30 p.m. (5:30 p.m. GMT), roads around the mall were blocked, the subway was stopped and a helicopter was flying above, said an AFP correspondent at the scene.

Heavily armed police officer kept onlookers back prevented locals from returning to their homes.

At the nearby Royal Arena, a concert with British singer Harry Styles was scheduled in the evening.

Shortly after the shooting, the organizer announced it would "proceed as planned," but later announced its cancellation, following criticism.

"My team and I pray for everyone involved in the Copenhagen shopping mall shooting. I am shocked," Styles said in a Snapchat post.

The shooting comes just over a week after a gunman opened fire near a gay bar in Oslo in neighbouring Norway, killing two people and wounding 21 others.

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