Thousands of anti-austerity demonstrators took to the streets of Athens on Wednesday as unions staged a general strike to protest the government's spending cuts and tax hikes, which some predict will push unemployment to a stunning 30 percent this year.

The 24-hour walkout disrupted flights, kept ferries and long-distance trains idle and crippled public services.

It was the first general strike of the year, renewing confrontation between labor groups and the conservative-led government that has pursued punishing austerity policies to cut debt, a key condition imposed by international bailout creditors.

State schools and tax offices closed down, public hospitals functioned on emergency staff, court cases were stalled as lawyers walked off the job, and even neighborhood street fruit and vegetable markets were cancelled. Private doctors and dentists also joined the strike.

In Athens, several thousand members of a Communist Party-affiliated labor union marched peacefully towards Parliament, while the main public and private sector unions were planning a separate march later Wednesday.

Previous protests have been marred by clashes between riot police and masked youths armed with fire bombs and stones. Up to 3,000 police officers were on duty for the street rallies.

Greece's largest union, the General Confederation of Greek Workers (GSEE), called for the strike, arguing that the labour force has been too badly weakened to pay emergency taxes.

According to union researchers, two-thirds of employees in the hammered private sector no longer receive regular pay.

Antonis Samaras, the country’s prime minister, has won praise from bailout lenders for pushing through major cost-cutting measures after forming a three-party coalition last June.

But a new round of tax increases this year and a surge in unemployment to 27 percent have angered unions, as Greeks battle a rapid increase in poverty during a fifth year of recession.

In recent weeks, the Samaras government has twice used rare emergency powers to force an end to strikes by workers on ferry services and the Athens subway.

A country of nearly 11 million, Greece now has the highest unemployment in the eurozone, with 27 percent out of work, including 60 percent of youths who have left school and are under age 24.

Since the country sank into recession in late 2008, a million people have lost their jobs, bringing the total number of unemployed to 1.35 million, according to official data for November 2012.

"The standard of living of the average Greek worker between 2009 and 2012, in a span of 36 months, has declined by at least 50 percent," said Savas Robolis, professor of economics and public policy at Panteion University in Athens, who is also the head of research at the GSEE.

Unemployment is expected to reach an alarming 30 percent this year, while national output will contract a further 4.1 percent, according to a study by a government funded research agency published last week.

Since losing market access in 2010, Greece has relied on emergency loans from other eurozone countries and the International Monetary Fund, and has opted for hefty benefit cuts and higher taxes on salaried employees to slash its deficits.

Meanwhile, on Wednesday, Bulgaria's government resigned from office after nationwide protests against high electricity prices, joining a long list of European administrations felled by austerity measures.

Prime Minister Boiko Borisov had tried to calm protests by sacking his finance minister, pledging to cut power prices and punish foreign-owned companies, but the measures failed to defuse discontent and protests continued on Tuesday.

Many Bulgarians are deeply unhappy over high energy costs, power monopolies, low living standards and corruption in the European Union's poorest country.

At least 25 people were taken to hospital after protesters clashed with police late on Tuesday.

"I will not participate in a government under which police are beating people," Borisov said as he announced his resignation on Wednesday.

The premier did not say if a parliamentary election scheduled for July would now be brought forward.

Borisov has said the electricity distribution licence of central Europe's largest listed company, Czech-based CEZ will be revoked, setting Bulgarian on course with its EU partner the Czech Republic.