"The site is 30 kilometres from our reserve and has caused great cultural and social impact in our community, not to mention environmental damage."
Armed with bows and arrows, people from eight tribes occupied the site at dawn on Sunday and confined the construction company's employees to their barracks.
There were no reports of injuries.
Talks between different Amazon tribes and the Aguas da Pedra power company broke down recently, triggering the takeover of the Dardanelos power plant, Globo News television said.
Paulo Rogerio Novaes, a company manager, said the indigenous were seeking access to better living conditions in the region and were trying to attract attention for their demands.
"These are problems the state needs to solve," he said.
Novaes said the plant, which is expected to be ready by the end of the year, would not directly affect the indigenous, and that the company was waiting for government approval for a series of community improvement programmes it plans to implement in the area.
The Dardanelos power plant is the first phase of the hydroelectric project Aguas de Pedra is undertaking in the western Matto Grosso state, which includes part of Brazil's vast Amazon jungle.