Turkish police had blocked all vehicle access and cut public transport to prevent protests on Taksim Square in the centre of Istanbul, the traditional focus for protests in the country's largest city.
Police moved in on the protesters close to the shores of the Bosphorus as they tried to head towards the square, using water cannon trucks and spraying tear gas, an AFP correspondent said.
This is the first May Day in Turkey, a national holiday in the country, to be marked after parliament passed a controversial security bill this year giving the police greater powers to crack down on protests.
President Recep Tayyip Erdogan's administration -- shaken by weeks of deadly anti-government protests in May-June 2013 centred on Taksim Square -- is hugely nervous about public demonstrations ahead of June 7 legislative elections.
More From This Section
By contrast, thousands of people packed into the centre of Athens in response to a call from public and private unions, joined by the country's controversial anti-austerity Finance Minister Yanis Varoufakis.
In Moscow, around 140,000 workers and students paraded on Red Square, waving Russian flags and balloons, a spectacle harking back to Soviet times.
In the Russian capital, some marchers wore T-shirts with the face of President Vladimir Putin while in Saint Petersburg others held portraits of Putin and wartime tyrant Josef Stalin and placards reading "Homeland, freedom, Putin."
Opponents of the project have accused the authorities of a needless waste of public funds by hosting the show at a time of austerity.
In South Korea, tens of thousands of workers held May Day rallies, vowing to wage an "all-out general strike" if the government pushes through with planned labour reforms.