Cuban President Fidel Castro staunchly defended his revolution in a May Day speech and attacked Latin American critics who have taken a more forceful stance on the island's human rights record as "lackeys" and "bootlickers" of the United States.
The veteran revolutionary, 75 and in power since 1959, addressed hundreds of thousands of people gathered in Havana's Revolution Square for the main event in Communist-run Cuba's annual celebration of the workers' holiday.
"To those who stupidly talk and repeat the imperialist refrain that there is no democracy and no respect for human rights in Cuba, I say no one can question that our country is today the most independent on the planet, the most just and supportive of other peoples, and also by a long stretch the most democratic," Castro said.
In Germany, one woman was fighting for her life after violence marking May Day erupted in two districts of Berlin. It began when a group of around 500 anarchists lit a large fire on a main street and then pelted firefighters with bottles and stones.
Police used water cannons against the demonstrators and hundreds of riot police moved in. Dozens of people suffered facial cuts from hurled bottles.
Authorities blocked parts of the city to demonstrators and sent extra police to other parts of the country to keep a lid on protests.
Almost every country in the world marks May Day in one way or another, and the date is officially recognized by the United Nations as International Labor Day.
Pro-Kremlin parties and trade unions stole the show from communists in Moscow by staging an estimated 140,000-strong rally in the Red Square -- something the country has not seen since the Soviet days.
In a message read out to the well-organized flower-waving crowd, Russian President Vladimir Putin welcomed the rally, which overshadowed a nearby communist demonstration demanding the government's resignation.
In the economically struggling former Yugoslav republic of Croatia, workers marched through the capital, Zagreb, to protest government plans to trim labor rights. Polish officials laid flowers at a monument in the city of Poznan to workers killed in 1956 anti-communist protests, but the capital, Warsaw, was calm as many people left for the countryside for a five-day weekend.
Workers in Macedonia handed out platefuls of hearty cooked brown beans - considered a laborer's staple - in the capital, Skopje, as they demonstrated for an end to poverty. The country has the highest jobless rate in the Balkans.
Communist authorities in China, which once derided private enterprise as evil capitalism, showed just how much things had changed by canonizing entrepreneurs as "model workers," awarding special medals to successful businessmen.
In the Swiss financial capital Zurich, police fired rubber bullets and tear gas in a bid to disperse a few hundred young radicals who defied a ban on protests after the official May Day workers' march.
Police doused demonstrators with water along the narrow streets of Zurich's red light district, while prostitutes enjoyed the show from the safety of their balconies.
In other cities around the world, trade unionists marched in traditional May Day parades, calling for better workers' rights.
A sea of red flags and banners transformed a medieval piazza in Bologna, northern Italy, as some 75,000 labor union members, many clutching red carnations, attended a Labor Day rally with the slogan: "For peace, employment, the defense of rights and against terrorism."
Malaysian authorities arrested 17 people in the capital, Kuala Lumpur, after labor activists marched through the city center with banners calling for better rights for plantation workers.
In Australia, where police arrested dozens of people after scuffles broke out at a picket line to protest against the country's immigration policies, union leaders expressed concern that their peaceful cause was being hijacked by fringe groups.
Greek protesters used May Day marches to denounce Israel's incursion into the West Bank, burning an effigy of Israeli Prime Minister Ariel Sharon outside the U.S. Embassy in Athens.
A huge workers' rally in the Syrian capital Damascus quickly turned into a show of solidarity with the Palestinians. "Sharon, you dog!" shouted some protesters.
In warm Italian sunshine, some 18,000 people gathered in front of the basilica of St. Peter's in the Vatican to listen to Pope John Paul II deliver his May Day audience.
"Today is Labor Day ... through work, man becomes more human. But for hard work to allow man to become more human it must always exist within a social framework," he said.
In the Philippines, 25,000 leftist workers and followers of disgraced former Philippine president Joseph Estrada marched on the heavily guarded presidential palace demanding the ouster of his successor, President Gloria Macapagal Arroyo.
Droves of anti-globalization and anti-pollution protesters clogged the streets of London with carnival-style protests including a picnic and a cycle ride, under the nervous eyes of police forewarned of possible anarchist attacks.
Elsewhere, hundreds of prostitutes took to the streets of Calcutta in India to press for rights and recognition.
One of the largest May Day turnouts was in France, where more than a million people took to the streets in a massive show of opposition to far-right presidential contender Jean-Marie Le Pen,
In Spain, the Basque separatist group ETA claimed responsibility for a car bomb that exploded near a Madrid soccer stadium hours before a European Champions League semifinal match. Madrid police said nine people were slightly injured in the blast, which destroyed several cars. There was no indication the blast was designed to coincide with May Day.
In a noisy, colorful duel of competing slogans and banners, labor foes and backers of Venezuelan President Hugo Chavez held rival May Day marches Wednesday, three weeks after a short-lived coup against him marked by bloody street protests.
Tens of thousands of Venezuelans took part in the separate rallies in Caracas. Around 1,500 officers policed the protests and occupied the high-rise rooftops from which unidentified snipers opened fire during a huge anti-Chavez march April 11, killing 17 people.