Some regions reported over 36 centimetres of rainfall over the past three days.
Aid slow to reach needy
The torrents swept away more than 40,000 houses, entire bridges and streets, as well as rail lines in 22 towns across Alagoas.
Power and phone services have been cut off in many areas and officials fear there could be many deaths unreported.
The federal government announced on Wednesday that it would send $56 million in supplies, including food and medicine. Officials say air force planes have already delivered 10 tons of supplies.
But local residents say the aid has yet to reach some of the hardest-hit areas.
"We're going hungry," Deise de Andrade, a housewife in the city of Uniao dos Palmares, told the AFP news agency. "Yesterday we had to pick food out of the mud to give it to my sons. We're eating mud."
In May 2009, flooding in the same area killed at least 44 people and displaced 380,000 others.