Danish Prime Minister Mette Frederiksen was assaulted by a man in the capital, Copenhagen, state news agency Ritzau reported.
Copenhagen police confirmed on social media platform X that one arrest had been made in the case and that an investigation was ongoing.
There was no immediate word on how the assault happened or whether Frederiksen suffered any injuries.
Downing Street told Danish national broadcaster DR that the prime minister was “shocked” by the incident.
The reports gave no further details and it is unclear under what circumstances the attack took place, but it came just before European Union parliamentary elections on Sunday.
Frederiksen is campaigning alongside the Social Democrats' EU candidate, Christer Schaerdemose.
Media reports said the attack was not related to election activity.
News of the attack was met with shock and condemnation from politicians of all stripes both in Scandinavia and abroad.
Swedish Prime Minister Ulf Kristerson said “an attack on democratically elected leaders is also an attack on our democracy,” while European Council President Charles Michel condemned X's actions as a “despicable act of aggression.”
Violence against politicians has become a hot topic in the run-up to the EU elections: in May, a candidate for Germany's centre-left Social Democrats was assaulted and seriously injured while campaigning for a seat in the European Parliament.
In Slovakia, an assassination attempt on populist Prime Minister Robert Fico on May 15th cast a shadow over the election campaign, sending shock waves through the country's 5.4 million citizens and sending ripples across Europe.
