About 300 Amazon Indians have prevented workers from entering or leaving the construction site of a hydroelectric plant that protesters say is on an ancient burial ground, according to reports from Brazil's official news agency.
Indians from eight tribes taking part in the protest, which began on Sunday, are demanding compensation for losses caused by construction of the Dardanelos plant in the southern Amazon city of Aripuana, according to Agencia Brasil.
"They want a sustainable programme in the region to make up for their losses in this archaeological site," Brazil's national Indian bureau coordinator, Antonio Carlos Ferreira Aquino, told the news agency.
The Indians have not resorted to violence since blocking the workers early on Sunday, but a plant manager told the government news service that he feared for the workers' safety.
A manager, Paulo Rogerio Novaes, said the Indians are seeking access to better living conditions in the region and are trying to attract attention to their demands. "These are problems the state needs to solve," he said.
Mr Novaes said the plant, expected to be ready by the end of the year, would not directly affect the Indians, whose nearest tribe is located about 25 miles away. The Indians say it is being built on a burial site.
Government officials were expected to arrive in the region to negotiate with the indigenous Brazilians.