Although numbers were lower than in previous years, thousands took to the streets in Spain, some brandishing flags reading "6,202,700", a reference to the record number out of work in the recession-hit country.
"This austerity is ruining and killing us," read one banner in Madrid, blasting the unpopular German-led policy of squeezing budgets in response to the eurozone's three-year debt crisis.
Jose Antonio Sebastian, a 50-year-old engineer, said he was one of the lucky ones still in work but feared he would soon be joining the ranks of the unemployed, now 27 per cent of Spain's working population.
Meanwhile, a strike in Greece stopped ferry services and disrupted public transport in Athens as workers marched against austerity in a country whose jobless rate is also around 27 per cent.
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Waving brightly coloured protest flags, nearly 13,000 people answered the call of unions and leftist groups to rally in the country, facing its sixth year of recession and making painful job cuts in efforts to appease international creditors.
Unemployment has reached a staggering 59 per cent among Greece's under-25s.
On Sunday, the Greek parliament voted to adopt a law that will allow the dismissal of 15,000 civil servants as part of austerity measures imposed by the indebted country's international creditors in return for desperately needed bailout funds.
In France, where unemployment has also hit a record high of 3.2 million people, the National Front party of extreme rightist Marine Le Pen, which also traditionally marches on May 1, called for a light of hope in a France "locked in the darkness of Europe".
Pope Francis used a private mass in his residence to mark May Day, urging political leaders to fight unemployment in a sweeping critique of "selfish profit" which he said "goes against God".