Hundreds of indigenous people and environmentalists have left the site of Brazil's $11 billion Belo Monte hydroelectric dam after occupying it to demand a stop to construction.

"We left peacefully, just like we came in. It was a peaceful action to bring attention on this deadly project for the Amazon," Eden Magalhaes, spokesman for Indigenous Missionary Council linked to the Catholic Church, said Friday.

Some 600 activists at the site of what would be the third biggest dam in the world -- after China's Three Gorges dam and the Itaipu dam on the border of Brazil and Paraguay -- had vowed to stay indefinitely.

But late Thursday, prosecutors in western Para state ordered the activists off the site following their day-long occupation and roadblock, in response to a request by the Norte Energia consortium that is building the dam.

"A judge arrived with shock troops. After consulting with one another, we decided to leave, but we are now more united than before in our opposition to the dam," Magalhaes told AFP.

"This project benefits big business. Local populations are suffering from the consequences and they are making a sacrifice of the forest."

The occupation sought a total halt to work on the project in Para, or at least a suspension of construction until local residents can be consulted.

A spokesman for the Xingu Forever Alive movement grouping indigenous peoples and locals of the Xingu basin vowed to plan more protest actions.

Construction on Belo Monte -- which would produce more than 11,000 megawatts, or about 11 percent of Brazil's current installed capacity -- has been the subject of legal wrangling for decades.

A federal court ordered construction halted last month, a decision hailed by the project's opponents as a "partial victory" pending a government appeal.

Environmentalists and Amazon Indian tribes say the dam will cause massive destruction of Brazilian fauna and flora in the area.

The project also has drawn international criticism, including from Oscar-winning movie director James Cameron of "Avatar" fame, who said rainforest indigenous tribes could turn to violence to block dam construction.

But the administration of President Dilma Rousseff has insisted the project should be allowed to go ahead, making it the centerpiece of government efforts to boost energy production in the rapidly growing economy.