Workers across the European Union have staged a series of protests and strikes against rising unemployment and austerity measures.
General strikes in Spain and Portugal halted transport and closed businesses and schools. Police and protesters clashed in several Spanish cities.
Rallies took place in 23 countries including Greece, France and Belgium, union officials told the BBC.
Hundreds of flights to and from striking nations were cancelled.
Airlines recommended that passengers check schedules before setting out to airports.
British Airways and Easyjet were among the UK carriers forced to cancel some of their services.
The European Trade Union Confederation has co-ordinated the Europe-wide action.
The confederation's Judith Kirton-Darling told the BBC that austerity was not working.
"It's increasing inequalities, it's increasing the social instability in society and it's not resolving the economic crisis," she said.
Some 40 groups from 23 countries were involved in Wednesday's demonstrations.
Unions in Spain and Portugal started strikes at midnight to protest against austerity measures that have combined tax rises with cuts in salaries, pensions, benefits and social services.
Marchers came out late on Tuesday in Spain, where 25% are unemployed, the highest rate in Europe.
"I have two sons in my house. One is getting subsidies, the other has been at home for the last three years," said protesting housewife Paqui Olmo.
"It is not that he doesn't want to work, there is just no work."
Picketers and police fought at a Madrid bus depot where demonstrators were trying to stop buses from leaving.
There were outbreaks of violence in other Spanish cities, and the interior ministry said more than 80 arrests had been made across the country. Dozens of people, including 18 police, were injured.
The government has played down the strike, saying the electricity grid registered 80% of its normal usage.
But unions claimed the operations of several large companies, including Danone and Heineken, ground to a halt.
In neighbouring Portugal, demonstrators took to the streets, carrying banners denouncing the European Union, International Monetary Fund (IMF) and European Central Bank (ECB).
The so-called troika has bailed out Portugal to the tune of 78bn euros ($100bn; £62bn), and demanded deep austerity measures in return.
The unemployment rate has hit a record 15.8%, according to figures released on Wednesday.
Prime Minister Pedro Passos Coelho acknowledged the rise was "bad news" but had been expected.
"We know that the unemployment level will increase a bit further before we observe a decline," he said.
Continue reading - BBC - European workers stage austerity protests
Read also: Reuters - Anti-austerity strikes sweep southern Europe
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