Tens of thousands of Polish labour union members have marched through the capital, Warsaw, in the finale of a four-day protest against the government.

The demonstrators threw smoke grenades and blew whistles as they marched to the historic Castle Square with banners saying, "Tusk's government must go," referring to Prime Minister Donald Tusk.

Saturday's protest reflects widespread public gloom over this year's sharp economic slowdown in Poland, which has been dragged down by the eurozone crisis.

We want the departure of Donald Tusk. This is the only way to change social policy in Poland. Marek Lewandowski, spokesman for trade union federation Solidarity

The disillusionment has plunged the coalition government's popularity to its lowest level since Tusk, Poland's longest-serving prime minister since the fall of communism in 1989, took office in 2007.

"We want the departure of Donald Tusk. This is the only way to change social policy in Poland," Marek Lewandowski, spokesman for the Polish trade union federation Solidarity, told the AFP news agency.

The marchers complained of large-scale layoffs after economic growth slowed down to 1.9 percent of gross domestic product last year from 4.5 percent in 2011.

They demanded job security, healthcare guarantees and retirement benefits, as well as the reversal of the recent raise of the retirement age to 67 years from 60 years for women and 65 years for men.

They have the support of a majority of Poles, according to an opinion poll carried out by MillwardBrown for the Fakty news programme on Tuesday: 59 percent of respondents said they were for the demonstrations, with 31 percent against and the rest unsure.

MP resignations

Unions also accuse Tusk of ignoring their demands and refusing to engage in dialogue.

Lawmaker Jacek Zalek, who quit Tusk's centrist Civic Platform on Thursday, told reporters the "protests were a sign that we were unable to rise to the challenges that were put before us by Poles".

In addition to Zalek, two of Tusk's MPs have also resigned in recent weeks, raising the spectre of a minority government that could spell early elections ahead of 2015.

But Tusk argued on Friday that his success in pushing through a revised 2013 budget, widening the deficit by an extra $5bn, bodes well for the future.

"Today's vote proves that the government's majority is stable," he said after Friday's vote, adding that concerns over the exodus of MPs are "unfounded".

Analysts said the vote suggested Tusk could still muster enough legislative clout to pass the 2014 budget and thus avoid snap elections.

Poland, with a population of 38 million, is the only EU member to have maintained growth each year for two decades.

However, the economy slowed to just 0.1 percent growth in the first quarter of this year as Poland's main trade partner, the eurozone, struggled with recession.