Trade unions and other groups staged rallies around the world to mark International Workers' Day with violence breaking out in Paris on the fringes of one protest.
Fearing France's worker protections are under threat, hundreds of angry youths on the sidelines of a rally hurled stones and wood at police in the capital, receiving repeated bursts of tear gas in response.
The traditional May Day rallies took on greater weight this year as parliament is debating a bill that would allow longer working hours and let companies lay workers off more easily.
The bill has prompted the most violent labour-related protests in a decade, with marches and sit-ins frequently degenerating into clashes with police.
Police encircled a few hundred suspected troublemakers on the sidelines of the Paris march on Sunday, and frustrated youth threw projectiles.
In Marseille, at least five people were arrested after scuffles with riot police. Marchers held banners calling President Francois Hollande a "traitor" and chanted "Everyone together!"
The Socialist government hopes the relatively modest labour reform will reduce chronically high unemployment and make France more globally competitive, by allowing companies more flexibility. Opponents say it erodes hard-fought worker protections and call it a gift to corporate interests.
In Russia, t ens of thousands of people marched across Moscow's Red Square in a pro-Kremlin workers' rally. The protesters were carrying the Russian tricolours and balloons.
As is typical for rallies organised by the ruling United Russia party, the May Day rally steered clear of criticising President Vladimir Putin or his government for falling living standards. The slogans focused on wages and jobs for young professionals.
Left-wing Russian groups held their own rallies.
This year the May Day coincided with the Orthodox Easter in Russia. Communist leader Gennady Zyuganov told Russian news agencies ahead of the rally that he celebrates Easter despite the Communist party's history of oppressing the Russian Church.
In Turkey, police used tear gas and water cannons to disperse dozens of May Day demonstrators in Istanbul.
Small scuffles broke out between police and demonstrators trying to reach Istanbul's Taksim Square. Taksim has symbolic meaning as the centre of protests in which 34 people were killed in 1977.
In the Istanbul districts of Sisli and Bakirkoy, police fired tear gas and water cannon to scatter other protesters. They also rounded up at least 36 demonstrators, according to Anadolu Agency.
The state-run news agency said police deployed around 15,000 officers and 120 water cannons in Istanbul, which has witnessed two suicide bombings this year.
May Day marches were held elsewhere in Turkey without incident but were cancelled in the southern city of Gaziantep after a car bomb attack on a police station.
In Manila, about 2,000 left-wing protesters scuffled with riot policemen, who used shields and a water cannon to try to prevent the flag-waving demonstrators from getting near the US embassy. Labour leaders said 20 protesters were injured.
Some of the protesters managed to break through the police cordon. TV footage in the Philippines showed some of them punching a retreating police officer and using wooden poles to hit a fire truck.
Police made no arrests and protesters dispersed after about two hours.
May Day rallies were held across the Philippines, with campaigning entering the final week ahead of the May 9 presidential election. Some of the candidates pledged to address labour complaints.
In T aipei, Taiwan's capital, labour unions took to the streets with a march to call on the government to reduce working hours and increase wages.
Many among the Taiwanese public have been concerned that outgoing President Ma Ying-jeou's push for closer economic ties with China has benefited just a few. Young Taiwanese have seen wages stagnate and good full-time jobs harder to find as the export-led economy has slowed.
Chen Li-jen, a protester with the Taiwan Petroleum Workers Union, said that while companies were seeing their earnings per share grow every year, workers' salaries were not rising in tandem.
"Hardworking labourers are being exploited by consortiums," Chen said.
"For the past decade, our basic salary has not made any progress," he said. "Labourers' rights have always been neglected. This is why I hope to take advantage of the May 1 Labour Day protest and tell the government that we are determined to fight for our rights."