Poland's nationalist Law and Justice (PiS) party narrowly won a second term in power, final results from Sunday's parliamentary election showed, but its drive to push through its conservative agenda may be hampered by a loss of the upper house.

PiS has campaigned on a promise to expand its massive welfare program and deepen reforms of the judiciary, an overhaul that has sparked unprecedented legal action from the European Union and drawn criticism of subverting democracy.

Speaking after a final count showed PiS had secured 235 seats in the 460-seat legislature, party chief Jaroslaw Kaczynski said, "Everything we consider important will be fulfilled, with all certainty."

The electoral commission said PiS had won 43.6 percent of votes, more than the 37.6 percent it secured in an election four years earlier.

Under Poland's complex electoral rules, the wider victory did not translate into any gains in the legislature. The main opposition grouping, the Civic Coalition, an umbrella organization that includes the Civic Platform (PO) formerly led by EU Council President Donald Tusk, secured 134 seats in parliament, with 27.4 percent of votes.

Four years of PiS rule have shifted the political climate in Poland, dividing the country over issues such as gay rights and media freedom, with critics saying PiS has fomented homophobia and turned public broadcasters into a mouthpiece for its agenda.

Tapping into widespread dissatisfaction with economic prosperity among many Poles since the collapse of communism, PiS told voters it aims to replace the business and cultural elites to ensure fair distribution of the nation's wealth.

Underlying divisions, election turnout at 61.7 percent was the highest in any parliamentary vote since a 1989 vote that ushered in the end of communism.

"There is a shift in the people's consciousness, which moves in the direction of blocking PiS's authoritarian tendencies," Izabela Leszczyna, a PO lawmaker who kept her mandate, said.

In a sign of an expanding political spectrum in Poland, three candidates from Poland's small Green party secured seats in parliament, as part of the Civic Coalition.

A brake

Electoral Commission data showed PiS secured 48 seats in the 100-seat Senate, meaning the opposition will have a chance to delay some its legislative efforts and have a say on the appointment of key officials such as some rate-setting members of the central bank and the civil rights ombudsman.

Coming on the day that Hungarian Prime Minister Viktor Orban, a key PiS ally, suffered his first defeat in about a decade by losing control of the capital Budapest, the result in Warsaw marked another setback for nationalists in the European Union who want to wrest back power from Brussels.

During its first term in power, PiS gained a reputation for pushing through legislation at breakneck speed, with hastily called late-night sittings of the Sejm, the lower house of parliament, followed by quick approval from the upper house.

PiS, which fought the election with pledges to defend patriotic and Catholic values and further increase welfare spending, had been hoping for a two-thirds majority of seats in the Sejm, which would have allowed it to reshape the constitution.

In a further sign of deepening divisions, a group of far-right politicians and activists, the Confederation, won seats in parliament for the first time, securing 6.8 percent of the vote, just above the 5 percent threshold needed to enter the legislature.

PiS had campaigned on a promise to enshrine more Catholic and patriotic values in public life, branding lesbian, gay, bisexual and transgender (LGBT) rights an "invasive foreign influence" that threatens Poland's national identity.