More than 1,100 people had to leave their homes and newborn babies were evacuated from a hospital.
On Saturday city officials warned that the death toll could rise. The provincial government said it was sending helicopters and ambulances as well as food and water, while the coast guard was helping in the rescue effort.
Authorities said more than 400mm (15.7 inches) of rain had fallen on BahÃa Blanca on Friday. The city normally receives about 600-650mm of rain a year.