People travelled from across Poland to attend the Warsaw rally against the government (Reuters)
Polish opposition leader Donald Tusk said "hundreds of thousands" of protesters had gathered in central Warsaw on Sunday to oppose the conservative government ahead of general elections on October 15.
Called by Tusk, the former premier and head of the centrist Civic Coalition bloc, the rally sought to mobilise the electorate for the crunch vote.
"When I see these hundreds of thousands of smiling faces, I have a good feeling that the breakthrough moment in the history of our homeland is coming," Tusk said.
"A great change is taking place -- this is a mark of the great Polish revival," Tusk told supporters who flooded the city centre, many holding Polish and European Union flags.
Participants began gathering in Warsaw in the early hours, with people travelling from across Poland to rally against the government.
Kazimierz Figzal said it took him seven hours to get to the capital from southwest Poland.
"We've had enough of what we witness now -- our freedom is being curbed. We want democracy, for our children and grandchildren," the 65-year-old told AFP.
Lech Walesa, a former Polish president, Nobel Peace Prize winner, and leader of the fight against communism, said earlier he planned to march, along with the leaders of some other opposition parties.
"We know what (the ruling party) fears the most -- the cooperation within the opposition," said Wlodzimierz Czarzasty, a co-leader of the New Left party.
The ruling party, which frequently clashes with the EU and faces accusations of undermining the rule of law, holds a comfortable lead in polls, with around 35 percent of voting intention according to IBRiS polling.
The Civic Coalition opposition alliance has long trailed in second place, with 27 percent of voting intention in the IBRiS poll.
But according to Tusk, internal polls commissioned by his own party show that the Law and Justice party's lead has narrowed to just two percentage points.
"The opportunity is within reach, nothing has been decided yet," Tusk told his supporters earlier this week as he addressed crowds in Elblag, northern Poland, promising to hold the authorities accountable following the vote.
"Many of them will go to jail for blatant theft, for violating the law and the constitution," he said.
Law and Justice leaders are holding their own rival rally in the southern city of Katowice on Sunday.
Bartlomiej Piela travelled from Katowice to Warsaw to take part in the opposition rally.
"Breaking fundamental civil rights and women's freedom to choose how they wish to live, pitting Polish people against each other... I hope the march will mobilise people to change it", the 29-year-old said.
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