Rio de Janeiro has declared a public health emergency because of an outbreak of mosquito-borne dengue fever just days before Carnival celebrations kick off across Brazil.

The outbreak wasn't expected to derail Carnival, which officially starts on Friday evening and runs until February 14, but it has prompted a slew of special measures by the city in hopes of containing the illness.

Rio city hall announced the opening of 10 care centres, the creation of an emergency operations centre and the allocation of hospital beds for dengue patients.

Authorities also will use "smoke cars" in regions with the highest incidence of cases, diffusing an insecticide in the air.

Since the beginning of 2024, the municipality has registered more than 10,000 dengue cases. That is just under half of the total cases - 23,000 - recorded throughout all of 2023.

The announcement comes as tourists and revellers are pouring into Rio to take part in street parties and attend the samba schools' flamboyant parades.

Among Rio state's operational plans for Carnival is the Against Dengue Every Day campaign. That will entail the distribution of repellents, stickers, bandanas and hats with warnings about the disease to audiences at the Sambadrome, where a 15-second notice about the fight against the infection also will be shown.

Dengue is a viral infection transmitted to humans through the bite of infected mosquitoes and is more common in tropical climates. Frequent rains and high temperatures, which accelerate the hatching of mosquito eggs and the development of larvae, make the famously hot city of Rio susceptible to dengue outbreaks.

But the problem is national. The explosion of dengue cases across Brazil has caused at least four states - Acre, Minas Gerais and Goias - to declare public health emergencies.