Denmark PM Mette Frederiksen has been left "shocked" after being attacked in the street in Copenhagen, BBC reports citing her office.

The assault took place on a square in the centre of the city where a man walked up to her and hit her.

The attacker has been arrested.

European Commission chief Ursula von der Leyen called it a "despicable act, which goes against everything we believe in and fight for in Europe".

"Prime Minister Mette Frederiksen was beaten on Friday evening at Kultorvet in Copenhagen by a man who was subsequently arrested. The prime minister is shocked by the incident," the prime minister's office said in a statement without giving further detail.

Police said they had arrested a man and were investigating the incident, but declined to say more.

There is no word on a motive yet.

Two witnesses, Marie Adrian and Anna Ravn, told local newspaper BT that they had seen the attack.

"A man came by in the opposite direction and gave her a hard shove on the shoulder, causing her to fall to the side," the two women told the newspaper.

They said that while it was a "strong push" the prime minister did not hit the ground.

She then sat down at a café, they added.

The attack comes two days before Denmark votes in the EU election.

Ms Frederiksen, leader of Denmark's Social Democrats, had earlier taken part in a European election event with her party's lead candidate Christel Schaldemose, Denmark’s TV2 reports.

The Social Democrats are the biggest party in Denmark's coalition government. They still lead the polls, but their support has fallen back considerably in recent months.