A knife-wielding assailant on Sunday stabbed the mayor of the Polish port city of Gdansk in front of hundreds of people at a charity event, police and media said.
Paramedics resuscitated Pawel Adamowicz, 53, at the scene before taking him to hospital where he underwent surgery.
"I learned that doctors succeeded in re-establishing the cardiac function of Mr Adamowicz who has been gravely wounded. There is hope but his condition remains serious," Polish President Andrzej Duda said on Twitter.
A video recording of the attack posted on YouTube showed the attacker bursting onto the podium.