In many countries, May Day - also known as International Workers' Day or Labour Day - is traditionally a time of political demonstrations organised by trade unions, anarchists, and socialist groups.
There were ugly scenes in Athens as protesters clashed with police during a rally called by trade unions and left-wing parties against the government's austerity measures to tackle Greece's enormous debt problem.
In the Chinese territory of Macau, police used water cannons and pepper spray against protesters who tried to break away from the approved route.
In Romania, thousands of left-wing protesters marched to the government headquarters in Bucharest demanding the resignation of the prime minister over the rise in unemployment and poverty.
Anger at rising unemployment and falling wages was also behind a mass rally in the Taiwanese capital.
In Scotland, protesters marched through Edinburgh's historic old town in an annual May Day rally over the war in Afghanistan and cuts to public services.
Far-left Ukrainian activists waved their fists and shouted anti-government slogans during a rally in Kiev.
Members of a banned Russian ultra-nationalist group, the National Bolsheviks, carry their flags during a rally in Moscow.
In Chile, clashes broke out between demonstrators and police as thousands marched through the streets of the capital Santiago.
In Los Angeles, protesters held a rally to condemn an anti-immigration law recently passed in the US state of Arizona.
The authorities in Cuba said that hundreds of thousands of people marched in Havana to voice their support for the country’s communist government.
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