The Polish city of Gdansk is holding a blood collection for its mayor, who remains in serious condition after being stabbed in the heart and the abdomen.
She said there was no immediate word about the mayor's condition at the hospital.
Adamowicz had been mayor of the Baltic port city for two decades and Civic Platform supported his reelection a year ago.
Polish broadcaster TVN reported the assailant shouted from the stage that he was imprisoned under the government of Civic Platform, a party to which the mayor formerly belonged.
Several Polish media outlets, including Rzeczpospolita, reported that the man yelled after stabbing Adamowicz: "Hello!"
Prosecutors said they would be pressing murder charges against the detained 27-year-old male suspect.
After doctors said Adamowicz needed a massive blood transfusion, hundreds of Polish donors came forward, according to Polish media. Hello! My name is Stefan, I was jailed but innocent.
"Goodbye Pawel, we'll remember you", Lech Walesa, Poland's legendary anti-communist leader and another native of Gdansk, said on Twitter.
Anti-violence rallies are being planned nationwide after yesterday's shock attack on Mayor Pawel Adamowicz.
Poland's health minister says that Gdansk Mayor Pawel Adamowicz has died from stab wounds a day after being attacked onstage by an ex-convict at a charity event. More than five hours after the attack there were no updates on his condition.
Video footage showed the attacker, who police said was wearing a press badge, bursting on to the podium and launching himself at Adamowicz, who had been waving sparklers with others on stage as the fundraiser was winding down on Sunday evening.
Dr. Jerzy Karpinski, the head doctor of the Gdansk region, told reporters Monday that the mayor is a "relatively young, healthy person with no health issues" and thus he was hopeful he would survive. Some said they were given time off work to help save Adamowicz.
The popular annual charity event for hospitals is traditionally cheerful and open, with celebrities, politicians and teenagers collecting money in the streets across Poland and also overseas. After leaving Civic Platform, he was re-elected to a sixth term as an independent candidate in the autumn.
As mayor, he is seen as a progressive voice.
Tusk, a fellow Pole born in Gdansk, was the late mayor's political ally. He showed solidarity with the Jewish community when the city's synagogue had its windows broken past year, strongly denouncing the vandalism.
At the time, Law and Justice was in the opposition and Kaczynski blamed the attack on an "atmosphere of hate" under rival party Civic Platform. A man ran to the stage and stabbed the official, claiming revenge for an injustice.