Poland's conservative ruling Law and Justice party (PiS) has won the most votes in the country's parliamentary election, according to partial official results.

The state electoral commission reported Monday that PiS won 44.6% of the vote. The opposition Civic Coalition, comprising the Civic Platform (PO) party formerly led by European Council President Donald Tusk and some smaller liberal parties, came second with almost 27%.

Other parties expected to surpass a 5% threshold to get into parliament were a left-wing alliance, which had 12% in the poll; the conservative agrarian Polish People's Party with nearly 9%; and the far-right Confederation with 6.8%.

The results were based on data from 99% of polling stations.

If confirmed, the return would mean that PiS can hope for an outright majority of 239 seats in the 460-seat lower house, the Sejm, Poland's main legislative body.

'We have a victory'

PiS party leader Jaroslaw Kaczynski declared victory on Sunday evening, while noting that the exit poll was not the final result.

"We have a victory: despite a powerful front, we managed to win," he said.

Voting closed at 9 p.m. local time (1900 UTC), but preliminary official results are not expected until later on Monday.

More than 30 million voters were choosing lawmakers in the Sejm and in the 100-seat Senate.

Read more: Poland votes: PiS and its pact with the people

Opposition parties aim to form coalition

The main opposition forces — the centrist Civic Coalition (KO), the Democratic Left Alliance (SLD) and the Christian Democrat agrarian Polish People's Party (PSL) — are hoping they can combine their support to beat PiS, allowing them to form a coalition government.

One of their common positions is a pro-EU stance and a pledge to undo controversial broad institutional reforms introduced by PiS over the last four years, including to the judiciary, which put the country at loggerheads with the European Commission.

Read more: How Sunday's election may impact Poland's economy

The PiS is the first party since the fall of communism to break with the austerity of previous governments, whose free-market policies took a waning communist economy and transformed it into one of Europe's most dynamic.

But many Poles were left out during that transformation, which lead to inequality and discontentment.

The PiS has skillfully addressed those concerns with popular programs, including one that gives 500 zlotys (€116, $128) to families per month per child, alleviating poverty for some and giving others more disposable income.

Orban offers congratulations

Hungarian Prime Minister Viktor Orban was one of the first to congratulate his Polish nationalist allies for their victory in Sunday's poll.

"There was a very important election in Poland from Hungary's point of view today, where the Polish ruling party has

secured a majority of seats in parliament and will be able to form a government on its own," Orban told a press conference. "We congratulate our Polish friends."

Orban has maintained a close relationship with the PiS in Poland, as they both hold serious grievances about how the European Union is run, particularly in terms of immigration.

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jsi, law/cmk (dpa, AP, Reuters)

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