Sao Paulo opened an emergency operations center Tuesday to deal with a surge in dengue fever cases that has hit Brazil and South America just as millions of tourists arrive for carnival celebrations.
Cases of the mosquito-borne disease have also risen sharply in Argentina, where a record 10,000 cases were reported in the first three weeks of the year.
Paraguay has meanwhile declared a health emergency over dengue. It has registered 36 deaths since December, including 12 children, officials there said.
Rio de Janeiro, Brazil's second-biggest city, after Sao Paulo, also declared a public health emergency Monday, four days ahead of the official opening of its famed carnival.
Authorities announced the opening of 10 dedicated treatment centers to alleviate pressure on Rio's overwhelmed hospitals.
"It's a good thing they opened this center. The hospitals can't handle the situation alone," patient Luciana Ferreira told AFP in the working-class Curicica neighborhood.
The capital, Brasilia, has opened an emergency field hospital.
Brazil registered 345,235 likely cases of dengue in the first five weeks of the year, nearly four times the number registered over the same period last year.
Thirty-one people have died of dengue, according to the Brazilian health ministry, which is still analyzing another 234 deaths that may have been caused by the disease.
Sao Paulo is testing a drone that uses larvicide to combat mosquitos in hard-to-reach areas.
Brazil plans to start a public vaccination campaign against dengue this month -- though a lack of doses from the vaccine's maker, Japanese pharmaceutical company Takeda, means only children ages 10 to 14 will be targeted.
Brazil's government says it is studying options to produce a dengue vaccine domestically.
Dengue, which can cause hemorrhagic fever, infects an estimated 100 million to 400 million people yearly, though most cases are mild or asymptomatic, according to the World Health Organization.