With black stripes painted on their faces and wearing ornate feather headdresses, scores of indigenous Brazilians set up camp Wednesday and promised to light up the rival gathering to the Rio+20 summit.

"The trip was exhausting but we came here to tell the world that we are being sidelined by society and the government," Antonio Terena told AFP after surviving a grueling 48-hour bus ride from the state of Mato Grosso do Sul.

"We are fighting for the demarcation of indigenous lands," said the 22-year-old tribesman as he reached Kari-Oca, an indigenous village set up in the Rio suburb of Jacarepagua for the "People's Summit" that opens Friday.

The Terenas -- the tribe name is used by all as a surname -- were preceded by 21 warriors from the Amazonian region of Xingu who set up large straw huts at Kari-Oca, which means "White man's house" in the Tupi-Guarani language.

The gathering of indigenous peoples aims forms part of a counterpoint to the official UN Conference on Sustainable Development, known as the Rio+20, which opened Wednesday but welcomes world leaders next week.

The "People's Summit," an initiative of 200 ecological groups and social movements from around the world, denounces the "green economy" concept being debated by 115 world leaders at the official June 20-22 UN meeting.

Some 400 representatives of 20 indigenous groups, including Guaranis, Tikunas, Tukanos, Gavioes, Kaiapos, Xavantes and Bororos are expected, along with 1,200 natives from Canada, the United States, Colombia and Nicaragua.

The UN conference marks the 20th anniversary of the Earth Summit -- a landmark gathering that opened the debate on the future of the planet and its resources.

"During the 1992 Earth Summit, the goal was to raise awareness of the importance of the environment. This time we are also going to show off our knowledge and traditions," 57-year-old Carlos Terena told AFP.

The tribesmen planned to light up a "sacred fire" overnight to attract good spirits ahead of the summit.

"We will light it up as our ancestors used to do, with tinders," said Carlos Terena.

He voiced concern about the future of the planet but said that development and preservation could still co-exist as long as "we grow less aggressively and make less profit."

The natives said they intended to share their experiences, debate the gains and losses of the last two decades and discuss their sacred relationship with Mother Earth.

A document resulting from their discussions will be submitted to the United Nations on Sunday.

One of the most contentious issues is the mining of mineral wealth found on indigenous lands.

Native interests received a boost on the eve of the summit as a Shell subsidiary that makes biodiesel in Brazil pledged not to buy sugarcane grown on the ancestral lands of the Guarani people.

The "People's Summit" will feature several different demonstrations, including a main march expected to draw 50,000 people on June 20, when the official Rio+20 meet gets under way.

A women's rally is scheduled for Monday along with a rally to protest a new forestry code in Brazil that would ease restrictions on forest protection and which environmentalists sees as a threat to the Amazon rainforest.