RIO DE JANEIRO — The governor of the Minas Gerais State in southeastern Brazil declared a public health emergency on Friday over an outbreak of yellow fever that appears to have killed at least 10 people so far and led to reports of more than 100 suspected cases of the disease.

The state authorities said Friday they were investigating 133 suspected cases of yellow fever, of which 20 were considered probable, pending further testing. They said they were also looking into reports of 38 deaths, 10 of them suspected of being caused by yellow fever, according to the State Health Secretariat’s website.

The state health authorities said the number of suspected cases had more than doubled in recent days: 48 suspected cases had been reported as of Wednesday, and that figure rose to 110 on Thursday.

According to the World Health Organization, yellow fever is an acute viral hemorrhagic disease transmitted by mosquitoes. Symptoms include fever, headache, muscle pain, nausea and vomiting. A small number of patients develop severe symptoms, and about half of those die within seven to 10 days.