From Moscow to Marseille, protests were expected in cities across the globe to celebrate Labour Day as the working classes battle economic crises and unemployment that have fuelled anti-government sentiment.

France was on high alert after protests against planned labour reforms this week descended into chaos with scenes of burning cars and stone-throwing protesters who injured dozens of policemen in Paris.

While government hopes the reforms will reduce chronic unemployment of about 10 percent, critics believe they threaten hard-won workers' rights by making it easier to lay off people in lean times.

Government has already watered down the bill but this has failed to calm the anger among students and workers demanding it be withdrawn.

French Prime Minister Manuel Valls on Sunday warned groups of troublemakers known as "casseurs" (breakers) who appear on the sidelines of marches actively seeking confrontation with police, leading to violent clashes.

"We will respond with the greatest of determination to these troublemakers ... the attacks and violence against security forces are unacceptable," said Valls.

Labour Minister Myriam El Khomri meanwhile defended her reforms, saying that debate on the bill should now shift to parliament where it is due in two days.

"This bill is fair and necessary," she told local media, adding that reformist unions who represent most workers were behind the changes.

Meanwhile in France, May Day celebrations exposed bitter divisions in the rising far-right National Front with former leader Jean-Marie Le Pen and his daughter and current party chief Marine Le Pen holding rival rallies.

Jean-Marie, 87, criticised his estranged daughter and predicted she would be roundly beaten in presidential elections in 2017.

- S.Koreans oppose 'evil bill' -

International Workers Day was started in Chicago in 1886 by a union demanding an eight-hour work day and is now celebrated around the world.

In South Korea -- also battling soaring youth unemployment -- planned labour reforms have similarly sparked anger among workers, and tens of thousands protested against the bill.

Labour activists say the reforms being pushed by President Park Geun-Hye and her conservative Saenuri Party will make it easier for companies to sack workers.

"Let's fight together against the evil bill!" activists and unionised workers chanted in unison during a protest in Seoul Plaza in front of City Hall.

In Moscow some 100,000 workers joined a May Day parade on Moscow?s Red Square, waving Russian flags and balloons near the Kremlin walls, police said.

The carefully choreographed spectacle harked back to Soviet times and took place amid a persisting economic crisis brought on by Western sanctions over Ukraine and low oil prices.

In Istanbul security measures were beefed up with some 25,000 police on duty and numerous roads closed for an occasion that regularly sees clashes between Turkish protesters and police.

Security was especially high at the main Taksim square, where demonstrators are expected to try and gather despite this being banned.

May Day comes at a time of particular tension in Turkey after a succession of deadly attacks this year blamed on jihadists and Kurdish militants.

Controversy is also growing over the rule of President Recep Tayyip Erdogan, whom critics accuse of increasingly authoritarian tendencies.

Several foreign missions have warned their citizens over the risk of violence in Istanbul on May 1, with the US embassy warning of the "potential for violent confrontation between demonstrators and security personnel".

On May 1 last year, Turkish police used water cannon and tear gas to disperse May Day protesters in Istanbul, while police and demonstrators engaged in pitched battles in some areas.

Parliament last year passed a controversial security bill giving the police greater powers to crack down on protests.

Taksim has been a flashpoint for clashes on Labour Day since dozens of people were killed there on May 1, 1977 when modern Turkey was going through one of its most turbulent periods.