The mayor of a Polish city is fighting for his life after being stabbed on stage during the finale of a charity fundraiser, doctors have said.

Pawel Adamowicz, mayor of Gdansk, grabbed his stomach and collapsed in front of the audience at the Lights to Heaven fundraiser organised by the Great Orchestra of Christmas Charity, the country’s most important charity.

Doctors transported him to Medical University of Gdansk, where he underwent five hours of surgery, Dr Tomasz Stefaniak, one of the doctors treating Adamowicz, said.

Police have arrested the suspect, a 27-year-old man who gave his name as ‘Stefan’.

Almost seven hours after the assault, Dr Stefaniak told reporters early on Monday that “the patient is alive”, triggering applause, but added that the mayor remained “in a very serious condition”.

“The next hours will decide everything,” he said, appealing for thoughts and prayers for the popular mayor.

After the knife attack, the assailant shouted from the stage that he had been wrongly imprisoned under a previous national government led by Civic Platform, a party to which the mayor formerly belonged.

He said his name was Stefan and that “I was jailed but innocent… Civic Platform tortured me. That’s why Adamowicz just died.” 

Mariusz Ciarka, a police spokesman, said the attacker appeared to have mental health problems and gained access to the area with a media badge.

TVN footage showed Adamowicz on stage with a sparkler in hand telling the audience that it had been a “wonderful day”, when the attacker came toward him.

European Council president Donald Tusk, a former Polish prime minister who co-founded Civil Platform and is from Gdansk, wrote on Twitter: “Let’s all pray for Mayor Adamowicz. Pawel, we are with you.”

Adamowicz, 53, has been mayor of Gdansk since 1998 and won 65% of votes in the 2018 regional election.

He was part of the democratic opposition born in that city under the leadership of Lech Walesa during the 1980s.

After leaving Civic Platform, he was re-elected to a sixth term as an independent candidate in the autumn.