To date condolences have been sent by the Israeli ambassador Anna Azari, the Mayor of Vilnius, Lithuania, Remigijus Simasius, the EP's European People's Party (EPP) and Alliance of Liberals and Democrats for Europe (ALDE) heads Manfred Weber and Guy Verhofstadt, Polish senior politicians and bishops.
The EP on Monday in Strasbourg observed a minute's silence in tribute to Adamowicz.
Sorrow over Adamowicz's death has also been expressed by Polish President Andrzej Duda and PM Mateusz Morawiecki.
"I join in sorrow and prayer with His Family, Friends and all People of good will. I ask God to support the Deceased's Family," President Duda wrote on Twitter.
"The murder of President Paweł Adamowicz is a great tragedy for all of us. It is a great evil that demands condemnation, great sorrow and regret. (I offer) the deepest expressions of sympathy for his despairing Family. Rest in Peace," PM Morawiecki tweeted.
The attacker, Stefan W., invaded the stage during the culmination of the 27th finale of the Great Orchestra of Christmas Charity (WOŚP) in the Baltic city of Gdańsk on Sunday evening, and stabbed the mayor. After making a statement through a microphone, he was overpowered by people on the stage and detained by police. (PAP)