The town of Trizidela do Vale is said to be almost completely flooded.
Across the north and north-east, some one million people are said to have been affected by the floods.
In Amazonas state, several rivers are still rising, officials said, including the Rio Negro which flows past the state capital, Manaus.
The Rio Negro is just 74cm (29 inches) below a record high set in 1953, the state-run Agencia Brasil news agency reported.
President Luiz Inacio Lula da Silva said the floods and drought in two southern states signalled climate change.
"Brazil is feeling climate changes that are happening in the world, when there is severe drought in areas that don't have drought, when it rains too much in places where it doesn't rain," President Lula said in his weekly radio address on Monday.
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