Labour activists have been holding marches and rallies in Europe and around the world to mark May Day, at a time of austerity and social unrest.
Politics coloured events in France - one of the eurozone's dominant states - which elects a new president on Sunday.
In Greece, which elects a new parliament the same day, a march through Athens passed off peacefully.
Thousands of Spaniards took to the streets of Madrid and Barcelona to protest against cuts and unemployment.
Scuffles broke out at a rally in the Italian city of Turin and there was some friction in the Greek capital, Athens but, in general, the demonstrations appeared to pass off peacefully in Europe.
Earlier, workers in Asian states marched for better working conditions and in North America, the Occupy movement has been holding events.
International Workers' Day, as the 1 May holiday is known officially, is meant to be a celebration of working people worldwide.
A recognised national holiday in most of the developed world, it is also celebrated unofficially in some countries.
In France, far-right leader Marine Le Pen refused to back either candidate in the country's presidential election run-off on Sunday, when she addressed supporters in Paris.
Ms Le Pen, who came third in the first round last month, said National Front voters should vote with their conscience, but added that both President Nicolas Sarkozy and his challenger, the Socialists' Francois Hollande, would surrender power to Europe.
Attacking Mr Sarkozy's five years in power and the ruling UMP party, she said she would "vote blank".
The National Front holds an annual march in Paris on 1 May to celebrate French heroine Joan of Arc.
Addressing a mass rally in Paris, Mr Sarkozy appealed for national unity around his Gaullist vision of France.
"I tell the unions, put down the red flag and serve France," he told the crowd at the Trocadero, which the UMP put at 200,000.
But the conservative leader also appeared to concede the banking system had been at fault.
"I want a new French model where the capitalism of the entrepreneurs will have replaced the capitalism of the financiers," he said.
Both Mr Sarkozy and Mr Hollande have been wooing the six million people who voted for Ms Le Pen in the first round.
In a speech in the town of Nevers, Mr Hollande voiced solidarity with trade unionists, saying: "When you have been a worker, when you have been a trade unionist, you know that inflation is a gnawing evil."
French trade unions were holding their traditional May Day marches in Paris and other cities.
Several thousand Greek workers, pensioners and students marched peacefully to parliament in central Athens holding banners reading "Revolt now" and "Tax the rich".
Greek Communist Party supporters gathered in the Aspropyrgos industrial area, outside Athens, to show support for workers at a local steelworks who have been on strike for months.
Anti-austerity protesters have been taking part in a day of strikes and demonstrations across Greece.
The BBC's Mark Lowen in Athens says the 1 May protests there have become an institution, with public and private sector strikes and disruption to public transport.
But he says there may be less of the traditional violence, since minds are focused on Sunday's general election, when many Greeks are expected to vent their anger against the austerity measures.
In Madrid, tens of thousands of protesters marched peacefully in the rain to the main square waving signs opposing government cuts.
The new conservative government is battling to prevent Spain needing an international bailout like those for Greece, the Irish Republic and Portugal.
"This day is an expression of rebelliousness... against the attack by the government upon the public services, upon employment, upon social and labour rights in our country," said Candido Mendez, head of the UGT union.
Ana Lopez, a 44-year-old civil servant, said May Day was sacred for her, but this year in particular because, she argued, the government was doing nothing to help workers and the economic crisis was benefiting banks.
"Money does not just disappear," she told the Associated Press news agency.
"It does not fly away. It just changes hands, and now it is with the banks, and the politicians are puppets of the banks."
In Russia, nationalists, communists and opponents of incoming president Vladimir Putin all held separate rallies in the former communist state.
Mr Putin and outgoing President Dmitry Medvedev made a rare joint public appearance on the streets of Moscow, leading more than 100,000 people in a Soviet-style "Holiday of Labour and Spring" march.
The Occupy movement has called for global protests against economic inequality.
The movement gained international attention with the Occupy Wall Street protest last September, but has struggled to maintain its profile as its supporters began to be evicted from public squares across the US.
An Occupy statement said: "The Occupy Movement has called for A Day Without the 99% on May 1st, 2012," referring to its slogan that the wealthy 1% rules over a powerless 99%.
Its main rally will be in New York in the afternoon rush hour.
The Occupy movement in San Francisco called for a Golden Gate Bridge protest.
It said: "This May Day we look forward to seeing strong, powerful picket lines, unlike anything the Golden Gate Bridge bosses have seen before."
Rallies took place across Asia:
- In Hong Kong, about 5,000 workers marched demanding a rise in the minimum wage
- In Jakarta, Indonesia, more than 9,000 workers marched to the state palace calling for better pay and job protection
- In Manila, the Philippines, some 8,000 workers rallied near the Malacanang palace to call for pay increases