Unusually heavy rains have fallen on an area stretching across parts of 10 of Brazil's 26 states, from the normally wet jungle to coastal states known for lengthy droughts.
The Brazilian military has evacuated thousands of people in the hardest-hit state of Maranhao.
In the northeastern state of Piaui, heavy rains continued to cause the Poty river to rise, flooding many parts of Teresina, the capital.
And in the interior region of Barras, entire communities have been left isolated and hundreds of thousands remained trapped in their homes.
Looting has also been reported in communities cut off by high water.
Luiz Inacio Lula da Silva, the Brazilian president, flew over the hardest-hit areas on Tuesday, delivering food baskets to shelters and meeting local officials.
Silva promised aid to repair infrastructure, and voiced concerns that global climate change could be responsible for the unusually heavy rains and destruction.