Violence erupted as a general strike in Greece crippled ferry, air and rail departures while a protest against pay cuts brought the Spanish capital's metro system to a halt.

With labour anger spreading across Europe over government spending cuts, the head of the Bank of France Christian Noyer said it may need up to 10 years of rigour to put public finances right again.

Greece was hit by a fifth general strike this year. A group of neo-Nazis tried to disrupt the main protest rally in Athens and police later fired tear gas as they were pelted with pieces of broken masonry by a few dozen protesters.

Police said seven officers were injured, six people were arrested and two banks and three shops had their windows smashed. In a separate incident, a policeman was taken away by ambulance after being hit by a stone.

A strong police guard enabled seven tourist ferries to leave Greece's main port at Piraeus, but then at least six ferry services were cancelled, the coastguard said. About 500 members of a communist union blockaded ships in the port.

A court declared the ferry strike illegal late Monday but the Communist party and its related syndicates shrugged off the ruling. Greece's main airlines grounded nearly 50 domestic flights while rail access to Athens airport was cut. Intercity trains also ran a reduced service along with hospitals while state offices shut down altogether. Journalists also joined the action.

More than 15,000 people took part in protest marches in Athens and the northern city of Thessaloniki, according to police. Unions said there were 35,000 demonstrators.

The labour unrest has cost Greece booking cancellations and millions of euros in damages at a time when the debt-hit nation is struggling to maximise revenues and revive its flagging economy.

Tourism contributes 17 per cent of Greece's gross domestic product and the government recently pledged to compensate travellers stranded in the country by strikes.

The demonstration in Athens, called by the country's main unions and leftist parties, attracted around 5,000 participants, police said. Some 4,000 people marched in the capital earlier at another protest called by Communist-affiliated workers.

A giant banner on a crane hanging over the protesters called on the Socialist government to scrap an austerity accord with the European Union and the International Monetary Fund in return for a huge bailout loan.

"When injustice becomes law, resistance is a duty," read another banner.

Unions have been particularly angered by the government's latest measure, which raises the general retirement age to 65 for men and women. It was to be discussed in Parliament yesterday ahead of a vote expected on July 8.

In Spain, a strike by Madrid metro workers forced millions of residents and tourists to find alternative transport to get to work and the main airport. The workers are protesting a wage cut of around five per cent imposed by regional authorities on the public sector.

Unions, protesting against a five per cent wage cut, refused to provide the minimum service normally used for such walkouts. Spanish media said it was the first time since 1991 that such a strike had paralysed the metro system, now used by around two million people daily.

Meanwhile with markets still tense over government debt levels, Mr Noyer, France's central bank chief, said it could take a decade to put public finances right without risking growth.

Asked how long measures to correct French public overspending would last, Mr Noyer told French radio: "I think it will take quite a few years, perhaps between five and 10 years probably."

He said: "Otherwise, if we want to go very quickly, that could have a negative effect on growth. We have to do it progressively, that will take at least five or six years."

Mr Noyer said households now fear that taxes will be massively raised and so they are saving money as a precaution.

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