Protesters across the world are taking to the streets to mark May Day, also known as Labour and International Workers' Day.
In Greece, the atmosphere at Saturday's demonstrations was tense, with millions of people facing increased taxes and pay cuts as the government struggles to overcome its huge debt problem.
Workers from Greece's two largest trade unions, Adedy and GSEE, marched through the capital, Athens, while workers belonging to the communist trade union, Pame, gathered in their thousands in front of the parliament building.
Riot police fired tear gas as they clashed with dozens of youths, some armed with sticks, near the finance ministry.
Skirmishes were also reported in other areas of Athens and in the city of northern city of Thessaloniki, where youths targeted cash machines and store windows with iron sticks.
Transport systems were crippled by strikes, with ferries docked in ports and passenger trains cancelled.
The port of Piraeus, which connects Athens with the Greek islands, was closed, with striking workers gathering to protest the government's planned spending cuts.
"They're trying to pass very reactionary measures," one protester said.
"They're trying to do away with all the rights we have gained through struggles in previous years."
Al Jazeera's Barnaby Phillips, reporting from Piraeus, said the labour movement in Greece feels under "direct threat to its livelihood".
The Greek government is set to announce sweeping spending cuts through 2012 to win support for an international rescue package worth $60bn in loans this year alone.
"There is no way foreign governments will be determined to help Greece unless they see determined efforts for the government to bring spending under control and realistic efforts to make its economy more productive," our correspondent said.
"Unfortunately many Greeks will pay the price for that process."
Clashes in Germany
In Germany, police said 13 officers had been injured when they clashed with 150 demonstrators who threw paving stones and set garbage cans ablaze in the northern port city of Hamburg.
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Several hundred officers were deployed in the capital, Berlin, as a neo-Nazi march and a leftist counterdemonstration went under way.
In Turkey, about 100,000 workers gathered at Istanbul's Taksim Square.
This year is the first time labour unions have been fully allowed to mark May Day at Taksim Square since more than 30 people died there in the so-called Taksim Square Massacre.
On May 1, 1977, shooting triggered a stampede in which dozens were killed.
The culprits were never found, contributing to instability which culminated in a military coup in 1980.
"Then human rights and especially workers rights were crushed for years in Turkey," Al Jazeera's Anita McNaught, reporting from Taksim Square, said.
"Over a serious of years, particularly the last three, the unions have steadily pushed and pushed to be reallowed access to back to this square.
"They have said there is no good reason not to allow them back and this year, the government agreed."
Police have deployed more than 22,000 officers for the rally and demonstrators were being searched before entering the square.
Zafer Yoruk, a professor of political science at Izmir University, said the number of workers organised in Turkish unions has fallen dramatically since the 1970s.
"Regarding unionisation and economic rights, I think we're far behind the 1970s," he told Al Jazeera.
"The rights to strike, for rights, or solidarity strikes, are totally gone."
Thousands of Cambodian workers marked May Day by marching through the capital to demand better work conditions and the establishment of a labour court.
Thousands of workers in the Philippines also took to the streets to reiterate their call to the government to protect jobs and to safeguard the interests of workers.
In the South Korean capital, Seoul, about 20,000 people gathered to demand better working conditions for labourers and farmers.
Source: Al Jazeera and agencies