Opinion polls suggest the nationalist Law and Justice (PiS) government could win the vote but may struggle to form a majority amid discontent among some over rising living costs and concern over an erosion of democratic checks and balances, Reuters reported.

Warsaw city authorities said about a million people attended in the capital's biggest rally on record. Public broadcaster TVP, which independent media observers say has become a government mouthpiece under PiS rule, quoted police saying about 100,000 people had joined.

Online news channel onet.pl said that according to its calculations some 600,000-800,000 people attended the rally.

TM/PR