Four toddlers and six adults have died after a security guard reportedly attacked a nursery school and began setting people alight.
Another 15 are reported to have life-threatening injuries. Forty people overall are being treated for burns, injuries and breathing difficulties, local media reported.
The incident took place at a daycare centre in Janaúba, in the north of Brazil.
Lieutenant Colonel John Aparecido Nascimento said: "The situation has caused a great deal of commotion in the city. We believe a security guard at the nursery set himself on fire and set fire to children in the kindergarten."
The attacker threw gasoline on himself, the children and the nursery before setting the whole room on fire.
He was taken to hospital with burns to around 90 percent of his body. There have been conflicting reports on whether he died.
The motive is yet to be confirmed by investigators. Local newspapers report he was recently fired from the nursery.
Hospitals nearby were overwhelmed by the attack, and five surrounding cities have sent emergency services to aid in the rescue.