Twenty-three people were arrested in connection with riots in Copenhagen, Danish police said on Monday, as counter-protests against a demonstration by a right-wing activist escalated.

The unrest spread on Sunday to several parts of the capital after Rasmus Paludan, the founder of the anti-immigrant party Hard Line, held a demonstration.

"I strongly disagree with Paludan's meaningless provocations that have no other purpose than sow disunity. Meet him with arguments - not with violence," Prime Minister Lars Lokke Rasmussen said on Twitter.

Police said they had arrested 23 people and some of them would be questioned by a judge later today about suspected arson and violence against police officers.