Poland deployed extra police in the capital Warsaw on Wednesday as thousands of far-right supporters, expected to include many from across Europe, gathered for the annual Independence Day march against a backdrop of political tension over the mass shooting in Krakow.

The Independence Day march has long caused friction between right-wing parties and the now-ruling centrists, who say it is a platform for racism and antisemitism. Participants deny those allegations, saying that the gathering, held under the motto "A Pole is the host in Poland," is an expression of national pride.

Prime Minister Donald Tusk appealed for restraint amid sharper-than-usual political divisions after ministers said the man who killed six people in the main square of Krakow may have been motivated by far-right ideology. "I address everyone, including those who will be gathering in Warsaw. We may hold different views, we may keep each other in check, and at times we may even be political opponents; yet, anyone who truly cares about Poland must understand that this space, defined by independence, freedom, and a secure Republic, is a common good," Tusk said in Szczecin in northwestern Poland.

Organizers say they expect a record turnout, with many foreign nationalists, including Spain's Revuelta, a youth movement linked to Vox, and members of the Hungarian far-right Mi Hazánk party. "We want a sovereign Poland, independent of foreign capitals ... We also envision a Poland that is as mono-ethnic as possible," said Rafal Buca, a spokesperson for the march organizers. Organizers urged people not to exploit the march for political ends and said they had condemned political attacks linked to the Krakow tragedy "regardless of whether they came from the right or the left."

Police said they had deployed more officers from outside the capital in Warsaw, declining to give numbers. Concrete barriers were installed on streets adjacent to the downtown starting point, while officers searched nearby areas. A crowd of thousands gathered under cloudy skies in a central square, many carrying large Polish flags. Authorities have in the past attempted to stop the march taking place following clashes between some of the participants and their political opponents or police.