A state of emergency has been declared in some areas.
Civil defence officials said food and drinking water were needed for at least 8,000 families.
Firefighters said food supplied by the federal government had distributed to 10,000 families.
Emergency shelters have been set up by the military for thousands of families.
The army has moved troops into several areas likely to be flooded by Amazon tributaries, like the Tapajos, as rain continues to fall.
Residents are using boats for transportation in some areas and are threatened by cobras and alligators.