A gunman opened fire inside a busy shopping mall in the Denmark's capital Copengagen on Sunday, killing three people and critically injuring three others, police said.

A 22-year-old Danish man was arrested after the shooting, Copenhagen police inspector S?ren Thomassen told reporters, adding there was no indication that anyone else was involved, though police were still investigating. He said the suspect was an "ethnic Dane", a phrase typically used to mean someone is White.

Danish police added?that he most likely acted alone and selected his victims at random.?Thomassen added?investigators do not believe the?attack was terror-related.

Thomassen said the victims included a man in his 40s and two "young people", without giving details. Several others were injured, three of them critically, he said.?

Thomassen later identified?three people were killed as?two Danish people?and one Russian citizen. He added?two Danes and two Swedes are hospitalised with serious injuries.

He further said it was too early to speculate on the motive for the shooting, which happened in the late afternoon at Field's, one of the biggest shopping malls in Scandinavia, located on the outskirts of the Danish capital.

Danish broadcaster TV2 published a grainy photo of the alleged gunman, a man wearing knee-length shorts and a tank top and holding what appeared to be a rifle in his right hand.

Images from the scene showed people running out of the mall, and TV2 posted a photo of a man being put on a stretcher. Witnesses said people were crying and hid in shops. After the shooting, an enormous contingent of heavily-armed police officers patrolled the area, with several fire department vehicles also parked outside the mall.

Copenhagen Mayor Sophie H Andersen tweeted: "Terrible reports of shooting in Fields. We do not yet know for sure how many were injured or dead, but it is very serious."

Laurits Hermansen told Danish broadcaster DR that he was in a clothing store at the shopping centre with his family when he heard "three, four bangs".?

He added, "Really loud bangs. It sounded like the shots were being fired just next to the store."

The shopping centre is on the outskirts of Copenhagen just across from a subway station for a line that connects the city centre with the international airport. A major highway also runs adjacent to the mall.

Singer Harry Styles was scheduled to perform on Sunday night at the nearby Royal Arena. CNN reported that the show has since been cancelled.?

On Snapchat, Styles wrote: "My team and I pray for everyone involved in the Copenhagen shopping mall shooting. I am shocked. Love H.”

Shortly after the shooting, the royal palace said a reception with Crown Prince Frederik connected to the Tour de France cycling race had been cancelled. The first three stages of the race were held in Denmark this year. The reception was due to be held on the royal yacht that is moored in Soenderborg, the town where the third stage ended.

The shooting came a week after a mass shooting in neighbouring Norway, where police said a Norwegian man of Iranian origin opened fire during a LGBTQ festival, killing two and injuring more than 20.

(With AP inputs)