A gunman has killed three people and injured another four at a shopping mall in Denmark's capital Copenhagen.

The victims are two Danish 17-year-olds and a 47-year old Russian. Two Danes and two Swedes were wounded - one remains critical.

Police said the suspected shooter, 22, had mental health issues and there is no indication of a terror motive.

The suspect, who was described as "an ethnic Dane" by police, will face questioning by a judge on Monday.

Prime Minister Mette Frederiksen said Denmark had suffered a cruel attack.

She said she wanted to encourage Danes to stand together and support each other in this difficult time.

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

The deadly shopping mall attack took place as Denmark celebrated hosting the first three stages of the Tour de France for the first time.

The suspect had a rifle and ammunition when he was arrested, police said.

They have no indication that other attackers were involved and urged shop owners to preserve any video surveillance footage they might have.

Field's has more than 140 shops and restaurants. The multi-storey mall is on the outskirts of Copenhagen, just across from a subway line that connects to the city centre.

Eyewitnesses spoke of panic among shoppers as gunfire rang out.

One of them, named Isabelle, told Danish media: "Suddenly we hear shots. I think I hear ten shots and then we run through the mall and end up in a toilet, where we huddle together in this tiny toilet, where we are around 11 people.

"It's really hot and we wait and we are really scared. It's been a terrible experience."

A concert by British singer Harry Styles at a venue less than a mile from the scene was cancelled.

Crowds had already gathered inside the venue when the show's cancellation was announced. Fans - many in their teens - were escorted by police to underground stations where parents picked them up, Danish media report.

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

"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.

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

Shortly after the shooting, the Danish royal family announced that a reception due to be hosted by Crown Prince Frederik to celebrate hosting the Tour de France's first three stages had been cancelled.