Tens of thousands of social activists and environmental and political groups have gathered in the Brazilian city of Belem for the World Social Forum.

The event is timed deliberately to coincide with the World Economic Forum in Davos, Switzerland.

Organisers say the global financial crisis has given the six-day meeting new importance in providing an alternative perspective.

Environmental issues are featuring prominently in the discussions.

Brazil's President Luiz Inacio Lula da Silva will join four other presidents from across South America at the forum later this week.

Amazon's future

The city of Belem, not far from the mouth of the Amazon River, is a location of symbolic importance for the tens of thousands of political and environmental activists who have gathered there.

The future of the Amazon itself is a key concern for those taking part in the World Social Forum, among them representatives of Brazil's Indigenous population.

There has already been a chaotic protest as Indian groups along with many thousands of demonstrators marched and danced through the streets of city, calling on the world to protect the rainforest.

The World Social Forum was first held in Brazil in 2001, and as in previous years the gathering has been timed to present an alternative view to the World Economic Forum at Davos in Switzerland.

The theme of the forum in Brazil is that "another world is possible" and that during a period of economic crisis for many countries the time is right for change.

The broadly-based gathering has attracted a range of individuals and groups from faith healers to communists and peace activists.

The economic crisis has undoubtedly raised the profile of the social forum. Local officials believe that as many as 100,000 people are in Belem for what organisers say has grown to become the biggest anti-globalisation event on the planet.