Two policemen were injured, one stabbed in the leg, and dozens of marchers were arrested after demonstrators attempted to blockade the Sydney stock exchange.
Clashes broke out in Australia and Germany, but for the most part the hundreds of thousands of people who took part saw no violence.
In Australia, about 30 people were injured after thousands of anti-globalisation protesters fought with police in Melbourne and Sydney, blockading buildings and burning political effigies.
Two policemen were injured, one stabbed in the leg, and dozens of marchers were arrested after demonstrators attempted to blockade the Sydney stock exchange.
Protesters in Brisbane threw themselves on the road to try to prevent police vans taking those arrested away.
"The world belongs to the people. The streets belong to the people," shouted protesters in Brisbane.
In Germany, riot police in Berlin clashed with anti-capitalist protesters in two separate locations in former east Berlin, one on the site of the Berlin Wall itself.
At least 40 people were arrested as police moved in with water cannon and armoured cars.
A rally by the the neo-nazi National Democratic Party (NPD) passed off peacefully on the eastern outskirts of the capital.
In Switzerland several dozen people were arrested in Zurich as left-wing demonstrators dressed in black and wearing hoods threw stones and bags of paint at the security forces.
In the UK, more than 6,000 police were deployed as thousands of people stage a series of an anti-capitalist protests in the heart of London.
London police have said they are adopting a policy of "zero tolerance" to prevent a repeat of last year's violence in the city.
In Zimbabwe, riot police moved in to break up trouble at a traditional May Day rally between trade unionists linked to the opposition, and self-styled war veterans backed by the government.
The war veterans, who have been attacking businesses in Zimbabwe's cities, say they can better represent the rights of urban workers.
In Pakistan, police have arrested more than 150 pro-democracy protestors in the port city of Karachi. They were attempting to defy a ban on public meetings imposed by the military regime.
Large numbers of police and paramilitary have been deployed on the streets.
In Russia tens of thousands of people marched to demand better pay and more jobs.
In Siberia and the Far East there were nationalistic tones as the marchers carried banners saying "We need a second Stalin" and "No to the anti-national policy of the government".
In South Korea, thousands of workers marched through Seoul to protest against economic reforms that have resulted in layoffs.
About 500 South Korean trade unionists also attended an unprecedented joint rally with workers in communist North Korea.
In Iran, workers demanded jobs and tougher action against illegal foreign labourers.
In Turkey relatives of left-wing prison inmates chanted anti-government slogans, holding banners reading "Stop to isolation". Twenty prisoners have died of hundreds who are on hunger strike.
Norway's Foreign Minister Thorbjoern Jagland was in for a surprise when protesters threw cream pie in his face.
He light-heartedly cleaned himself up and proceeded to lead a labour march in Oslo.