A wave of anti-austerity anger breaks out across Europe on Wednesday, with general strikes in Spain and Portugal spearheading a day of protest that will ground more than 700 flights.

Growing angst over public spending cuts and tax increases is being exposed in particular in debt-struck eurozone economies already suffering high unemployment and recession.

Clashes between riot police and protesters have broken out in stricken eurozone states such as Greece and Italy, and less frequently in Spain, now grappling also with the despair of evicted home-owners.

Rallying behind slogans such as "They are taking away our future!" and "There are the guilty, there are solutions!," Spain's main CCOO and UGT unions called a second general strike in eight months.

Airlines operating in Spain, including Iberia, Iberia Express, Air Nostrum, Vueling, Spanair and easyJet cut more than 600 flights including some 250 international routes. Ryanair said no flights had been scrapped yet.

Dozens of protests by unions and activists are planned across Spain, the fourth-biggest eurozone economy, which is tightening its belt as it ponders seeking a sovereign rescue.

Activists called on social networks for an evening rally outside the parliament in Madrid. The action comes as Spain's right-leaning government and Socialist opposition are discussing how to combat a surge in home-owner convictions, blamed for two suicides in just 15 days.

Neighbouring Portugal, where protesters booed visiting German Chancellor Angela Merkel on Monday when she came to support Lisbon's austerity policies, will also hold a general strike.

Protests are being called in some 40 towns and cities across the bailed-out nation, including Lisbon and Porto.

Portugal's TAP said it was grounding more than 160 flights, most of them international.

Greece, struggling to satisfy international lenders that it has cut spending sufficiently to qualify for bailout funds and to avoid default, has called a three-hour work stoppage and a rally in Athens.

Italian unions, too, are seeking a four-hour work stoppage.

The European Trade Union Confederation said it was the first time that it had appealed for a day of action that includes simultaneous strike action in four countries.

"By sowing austerity, we are reaping recession, rising poverty and social anxiety," the union confederation's general secretary Bernadette Segol said in an online statement.

"In some countries, people's exasperation is reaching a peak. We need urgent solutions to get the economy back on track, not stifle it with austerity. Europe's leaders are wrong not to listen to the anger of the people who are taking to the streets."

Short of taking full strike action, unions and activists in other European countries say they, too, plan to support the so-called "Day of Action and Solidarity".

Union-led rallies are being called across France and in Poland, where workers decry a "social and wage-dumping" in their country.

In Germany, viewed by many in southern Europe as the paymaster behind the austerity drive, the union federation DGB has called protests across the country including in Berlin and Frankfurt.

"For now it is mostly people in southern Europe suffering from a crisis they are not responsible for. But the consequences will surely be felt in the rest of Europe," the union grouping said in a statement.

High-speed Thalys rail services between Belgium and Germany have been cancelled for the day.