Demonstrators protest against budget cuts in Ljubljana. (Srdjan Zivulovic/Reuters)

More than 30 people are facing charges in Slovenia, police said Saturday, for clashing with police during anti-government protests in the capital that left more than 15 people injured and fueled tensions on the eve of a presidential election in the economically struggling EU nation.

The demonstrators, who were detained after Friday's clashes, have been released pending further investigation, police spokeswoman Maja Ciperle Adlesic. The 33 people been charged with violating public order and will face further charges for attacking police, she said.

About 8,000 people joined the demonstrations in Ljubljana against Prime Minister Janez Jansa's government and its cost-cutting measures drafted to avoid an international bailout for the financially troubled Slovenia.

Police said violence erupted at the end of the gathering when about 100 violent extremists threw rocks, and police responded with water cannons and tear gas. The hooded, young demonstrators then fought street battles with the police throughout the city centre.

The clashes in Ljubljana were the second this week, after a rally in the second-largest city of Maribor against the local mayor also turned violent. Violent protests are highly unusual in the otherwise calm Alpine nation, triggering fears Slovenia's economic crisis could push the country into instability.

Police said many of the demonstrators were underage and some already have criminal records. Local media reported they are members of far-right and hooligan groups, which have mushroomed in Slovenia because of the crisis.

"We never had riots like this against police in Slovenia," spokesman Vinko Stojicek said. "We will analyze the behaviour and draw conclusions."

Local media said more protests are planned for next week in both Ljubljana and Maribor.

Pension reforms, public sector cuts

Slovenia is facing one of the worst recessions of the 17 eurozone nations. Its economy has shrunk more than 8 per cent since 2009 and continues to decline, resulting in a sharp drop in exports and living standards and a surge in unemployment, which now stands at about 12 per cent.

Jansa's centre-right government has launched pension and labour reforms and cut salaries in the public sector as part of an austerity package. The reforms have somewhat been stalled because of political bickering among the divided leaders.

The protesters in Ljubljana on Friday carried banners that read "He is Finished" or "Thieves," urging the ouster from power of Jansa's government whom they accused of corruption.

"We are all fed up," 36-year-old Leon Kores, whose salary in a kindergarten has been slashed with the austerity package, said on Saturday. "They have all been stealing from us, and now when there is no more money we will pay the price."

The presidential runoff on Sunday is pitting incumbent Danilo Turk against former prime minister Borut Pahor, who is tipped to be the frontrunner. Pahor has supported some of Jansa's reform measures, while Turk has been highly critical.