The mayor of the northern Polish city of Gdansk has been stabbed while on stage at a major charity event, officials say.
Pawel Adamowicz, 53, had to be resuscitated after the attack and is reportedly in a critical condition in hospital.
The suspect, a 27-year-old local resident with a criminal record, has been detained.
He had access to the scene using a media badge, Polish media report.
The incident took place at the country’s biggest annual charity event, the Great Orchestra of Christmas Charity, which was attended by hundreds of people.
The suspect reportedly shouted that he had been wrongfully imprisoned under the previous government, led by the mayor’s former party.
The stabbing, during an event that raises money for children’s hospitals, has shocked Poland, the BBC’s Adam Easton in Warsaw reports.
Mr Adamowicz is a well-known political figure who has been mayor of Gdansk for 20 years, our correspondent adds.
Interior Minister Joachim Brudzinski said the attack was “an act of inexplicable barbarism”.
Prime Minister Mateusz Morawiecki said on Twitter: “The attack on life and health of Paul Adamowicz is worthy of the highest condemnation.”
Also on Twitter, President Andrzej Duda said: “I pray for his return to health and full strength.“