More than 150 fishermen and indigenous natives occupied Brazil's Belo Monte dam on Tuesday, claiming the project will do irreparable damage to the Amazon ecosystem and their way of life.

"This singular alliance of Indians and fishermen is aimed at blowing the whistle on the construction company which has not kept promises made in June, during the Rio sustainable development summit," Maira Irigaray, spokeswoman for the "Xingu Vivo" movement, told AFP.

Irigaray said the fishermen had teamed up with members of the indigenous Xipaia, Kuruaia, Parakana, Arara, Juruna and Assurini peoples.

"They occupied the Pimental construction area where the Xingu River already has been dried up," she said, adding that the demonstrators would stay "until their demands have been met."

The indigenous people snatched keys for trucks and bulldozers and workers left the area on foot. Protesters said their demonstration was peaceful.

Protesters accuse Norte Energia, the consortium behind the project, of backtracking on accords signed in June when 150 indigenous people occupied the Pimental area for three weeks.

The native peoples want their lands demarcated and non-indigenous folk removed from them, as well as a better health care system and access to drinking water.

Indigenous groups fear the dam will harm their way of life while environmentalists have warned of deforestation, greenhouse gas emissions and irreparable damage to the ecosystem.

"Avatar" director James Cameron and actress Sigourney Weaver have given their backing to dam opponents, drawing parallels with the natives-versus-exploiters storyline of their blockbuster Hollywood movie.

Belo Monte is expected to flood an area of 500 square kilometers (200 square miles) along the Xingu, and displace 16,000 people, according to the government. Some NGOs estimate that 40,000 people would be displaced.