The mayor of Polish port city Gdansk was stabbed while on stage at a charity event.
Footage which claims to have been shot during the event, shows the incident happened in front of a large, celebrating crowd.
Pawel Adamowicz was rushed to hospital following the attack in a serious condition.
Mr Adamowicz was attacked with a sharp tool during the “Light to Heaven” event, spokeswoman Magdalena Skorupka-Kaczmarek said.
Interior Minister Joachim Brudzinski said Mr Adamowicz called the stabbing “an act of inexplicable barbarity.”
A suspect has been arrested, Mr Brudzinski said.
YouTube video appears to show the moment the terrifying attack took place.
People can be seen waving what look to be sparklers on stage as people in the crowd cheer.
A man then jumps on stage and appears to attack Mr Adamowicz. He remains pacing on stage with his hands in the air, as music continues to play.
It’s understood a knife was used in the incident.
Polish broadcaster TVN claimed that the attacker shouted that he had been imprisoned under the government of Civic Platform, a party to which the mayor formerly belonged.
Mr Adamowicz had no direct involvement in the man’s imprisonment.