Rio De Janeiro: With placards, balloons and chain saws, thousands of activists staged a good-natured and colourful protest in central Rio on Wednesday against the UN Rio+20 summit on a “green” economy.

The march drew environmentalists, workers, civil servants, militants, homosexuals, indigenous peoples and feminists on the day world leaders kicked off the UN summit on sustainable development.

Organisers said 50,000 people turned up but police estimate the crowd at no more than 20,000.

The protesters came to denounce, among other things, Amazon rainforest deforestation, the plight of indigenous peoples, poor salary conditions of public employees and capitalist attempts to hijack the "green economy".

The event was organised by 200 civil society groups attending the "People's Summit" being held as a counterpoint to the official Rio+20 summit that runs through Friday.

"Rio+20 represents a retreat and a bid to turn nature into a commodity," said Ana Elisa Bacellar, a 34-year-old civil servant sporting fitted with a clown's nose and handcuffs.

There was a huge Brazilian flag and an effigy of Brazilian President Dilma Rouseff with hands up.

A performance by the NGO The Spoon Revolution showed a woman dressed as planet Earth being flogged by a big landownwer shouting "more meat for the United States" while his employee, wearing a blood-stained apron reading "Mac Killer" and "Murder King" chases a dummy cow with an ax.

"We are fighting to change consumption habits and against big food companies," said Mariana Terra, a 23-year-old history student who planned the show.

Greenpeace activists shouted: "Who does not jump is a ruralist," in a direct criticism of the pro-agribusiness bloc that pushed for reform of Brazil's forest code.

Rousseff last month vetoed parts of the new forest code that environmentalists said would have increased deforestation in the Amazon.

The new code maintains a requirement to protect 80 per cent of the forest in rural areas of the Amazon and 35 per cent of the sertao, or arid hinterland of northeastern Brazil.

But it eases restrictions for small landowners who face difficulties in recovering illegally cleared land.

Also demonstrating were some native Guatemalans who are in Rio along with some 1,600 other indigenous peoples from around the world attending the People's Summit.

"We are here to defend the natural resources and the territories of our people, threatened by mining interests and hydro-electrical," said a 40-year-old Guatemalan woman wearing a colourful skirt.

Activists from Brazil's black and gay communities also marched to demand a radical transformation of the world economy while a group of South Koreans railed against nuclear energy.

"We want world leaders present here to promote sustainable development and poverty eradication and cut nuclear weapons," said Nam Boo Won, an official representing 21 South Korean environmentalist groups.

Also parading was a gyrating samba queen in golden sequins, escorted by a life-sized bread tank with a garden inside to underline the realistic possibility of eradicating hunger and extreme poverty by redirecting military spending.

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