Paweł Adamowicz, mayor of the northern Polish city of Gdańsk, has died due to his injuries from a stabbing attack onstage in front of hundreds last night which has left Polish people shocked.

Adamowicz had been on stage for the finale of the Great Orchestra of Christmas Charity, Poland’s largest of its kind which raises money for children’s healthcare. As pyrotechnics illuminated the stage, an assailant rushed up to the mayor and stabbed him with a knife, causing severe damage to his heart and diaphragm.

The attacker – Stefan W., a 27-year-old Polish man with a criminal record for bank robbery – then briefly shouted into the microphone that he had been unfairly imprisoned by PO (Platforma), Adamowicz’s former political party. He was quickly tackled and taken into police custody.

Event organizers say the attacker was able to get onstage with a press pass, although it is unclear how he was able to obtain it.

The mayor was rushed to the nearby Medical University of Gdańsk, where doctors performed a difficult five-hour operation in which 41 units of blood were used. They announced that he was in critical condition and living on the support of a breathing machine.

At 14:30 today, he was pronounced dead at age 53.

In response, Poles flocked to blood donation centers in order to lend their support, and outpourings of grief and support came from around Poland and the world. Krakow mayor Jacek Majchrowski said he was “shocked” and offered his thoughts for Adamowicz’s family. Jerzy Owsiak, head of the charity, blamed the attack on an atmosphere of hate fostered by the nationally ruling right-wing Law and Justice (PiS) party.

Paweł Adamowicz was born in 1965 in Gdańsk. In high school he joined the Solidarity movement against the communist government of the time and worked in the underground press. He served as mayor of his city – now home to around 464,000 people on the Baltic coast – for the last 20 years over six terms. He is remembered as a champion of minority causes – for example, last year supporting Gdańsk’s Jewish community after a synagogue’s windows were broken and participating in the city’s fourth annual LGBTQ pride march last year.

Following his death, his deputies automatically lose their positions, and Polish prime minister Mateusz Morawiecki will appoint a temporary mayor until new elections can be held.