Children from five continents held aloft a banner that proclaimed: "Another world is possible," as militants marched through the southern Brazilian city, marking the start of their six-day World Social Forum (WSF).

The eclectic gathering of pacifists, environmentalists, libertarians, trade unionists and anti-establishment militants was timed to coincide with its nemesis, the World Economic Forum held thousands of kilometers (miles) away in the swank Swiss mountain resort of Davos.

The more than 50,000 demonstrators set off in Porto Alegre just a few hours after the opening of the Davos summit, which anti-globalization activists denounce as a celebration of crass capitalism.

Organizers said some 100,000 participants will take part in the fifth annual WSF, which features hundreds of workshops dealing with issues such as debt, poverty and development.

In some cases the issues will be highlighted in connection with the December 26 tsunamis that hit 11 south Asian countries. Participants were to observe a minute of silence for the more than 280,000 victims of the devastating tidal waves.

Beverly Keene of the Jubilee South group said the six billion dollars pledged by the leading industrialized countries for tsunami relief efforts in Asia were only a fraction of what major powers used for "war and destruction."

"It is outrageous compared, for example, with the annual US military budget of 400 billion dollars, or with the 200 billion dollars already spent in Iraq by the United States and other coalition members," she said at a news conference.

Nobel Peace Prize laureate Adolfo Perez Esquivel, for his part, called for the unconditional scrapping of impoverished countries' foreign debt.

"The debt of the poorest countries is social genocide. Its elimination is an urgent necessity," said Perez Esquivel, from Argentina.

On Thursday, more than 1,000 non-governmental organizations will appeal to world leaders to do more to battle poverty. They will launch a campaign to back the UN Millennium Development Goals to cut poverty by half by 2015.

Brazilian President Luis Inacio Lula da Silva was to participate in Thursday's session.

His culture minister, popular singer Gilberto Gil, also will join the forum, whose program includes artistic performances, an indigenous "ritual of sacred fire" and the discussion of esoteric issues such as "ethics and cosmovision."

The vast majority of participants came from Brazil, the United States, France and Italy, but a significant number of Asian activists also were at the forum, according to organizers.

The WSF was born in 2001 in Porto Alegre, two years after the anti-globalization movement was galvanized in the US city of Seattle, Washington, where some 40,000 protesters wreaked havoc during a World Trade Organization gathering.

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