Updated 2.17PM: A gunman has killed at least one person and wounded three police officers after opening fire on a cultural centre in Copenhagen as it was hosting a debate on Islam and free speech.

Swedish artist Lars Vilks - the author of controversial Prophet Mohammed cartoons that sparked worldwide protests in 2007 - was among those at the debate targeted by the gunman, who fled the scene after a shootout with police.

Danish Prime Minister Prime Minister Helle Thorning-Schmidt described the assault as "a terrorist attack" as Danish television showed the windows of the Krudttonden cultural centre pock-marked by multiple bullet holes.

Police released a photo of the suspect showing a man in a dark anorak and a maroon hat carrying a black bag.

They described him as 25-30 years old, around 185cm tall, with an athletic build.

French ambassador to Denmark Francois Zimeray, who had been present at the debate but was not hurt, said the shooting was an attempt to replicate the January 7 attack against the Charlie Hebdo weekly in Paris, which left 12 people dead.

"They shot from the outside (and) had the same intention as Charlie Hebdo, only they didn't manage to get in," he said.

"Intuitively I would say there were at least 50 gunshots, and the police here are saying 200.

"Bullets went through the doors and everyone threw themselves to the floor."

A statement by Danish police said "an unidentified man died after having been hit by bullets" in the strike, and three officers were wounded in the shooting.

Police initially said two suspects had fled the scene in a Volkswagen Polo. The car was found abandoned around two hours after the attack.

After witness statements indicated there was just one attacker, police later said they were hunting for a lone gunman.

Media reports said it was likely the gunman used an automatic rifle to fire as many rounds as possible in a short time.

"Denmark has today been hit by a cynical act of violence. Everything leads us to believe that the shooting was a political attack and therefore a terrorist act," the Danish premier said in a statement.

The assault comes at a time of heightened security and rising fears of Islamist attacks, following January 7-9 incidents in Paris that left 17 people dead.

Anti-terror sweeps carried out across Europe since mid-January have resulted in the arrests of dozens of suspected jihadists and seizures of large stocks of weapons and explosives.

Raids in Belgium on January 17 thwarted what police called imminent "terrorist attacks to kill police officers on public roads and in police stations."

Two suspects were killed fighting Belgian police in those sweeps.

Satirical weekly Charlie Hebdo raised the ire of Islamist extremists by publishing cartoons mocking Mohammed and periodically satirising Islam.

Vilks has been living under police protection after his controversial cartoons prompted death threats.