Tens of thousands of nationalists marched in Warsaw on Saturday to commemorate Polish Independence Day.
The demonstration was carried out under the slogan "Poland is not yet lost," a reference to the country's national anthem. It began in the city center on Saturday afternoon and was scheduled to end at the National Stadium.
Many participants held up white and red flags, while others carried hand flares.
Warsaw's municipal administration estimated the number of participants to be at least 40,000.
Organizers called the event the "largest patriotic rally in Europe."
Warsaw mayor Rafal Traszkowski said that the event occurred "peacefully."
PiS loses majority, unlikely to form government
The event comes after Poland's nationalist Law and Justice party (PiS) lost its absolute majority in parliament in an election last month, leading to its likely replacement by a left-leaning opposition alliance.
While the current ruling party won the most seats in the election on October 13, it lacks willing and viable coalition partners.
Opposition leader and Donald Tusk, who might well ultimately become the next prime minister, called for moderation in an Independence Day video message on social media.
"Anyone who uses the word nation to divide and sow hatred is standing against the nation," he said.
Current PiS Prime Minister Mateusz Morawiecki will have the first shot at forming a government after last month's elections, following a decision by President Andrzej Duda this week.
However, he is unlikely to win a confidence vote in the lower house of parliament, the Sejm. Even with likely allies like the far-right Confederation party, PiS would not command a majority in the Sejm.
Should he fail, parliament would suggest the next candidate prime minister, most likely Tusk, whose chances of winning the vote appear better.
Tusk's liberal Civic Platform (PO) has entered coalition negotiations with two other parties: the center-right Third Way alliance, which includes the agrarian Polish People's Party and the new Poland 2050 party, and the progressive Left party.
sdi/msh (AFP, AP, dpa)