A shooting at a school near Sao Paulo on Wednesday left 10 people dead, state military police said, before the two shooters turned their weapons on themselves.
Sao Paulo Governor Joao Doria said as he stood outside the school that "our solidarity goes out to the families of the victims".
Around 15 others were injured in the shooting, which took place at the Raul Brasil public school in Suzano, on the outskirts of Sao Paulo in southeast Brazil.
Marilene Gonçalves, a 51-year-old housewife, said she saw children fleeing the school, and that she gave safe harbour to several, including one boy who was shot in the jaw. He said authorities didn't believe the two were former students.
Latin America's most populous nation has the largest number of annual homicides in the world, but school shootings are rare.
President Jair Bolsonaro ran on a platform that included promises to crack down on criminals, in part by expanding public access to guns.
Police say they found a revolver, a bow and arrow and items that appeared to be explosives inside.
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"Then a lot of kids started running out, all screaming", he said.
He said it was not yet known whether the two assailants were former pupils at the school.
"When I arrived at the school.it was chaotic".
The last major school shooting in Brazil occurred in 2011, when 12 students in Rio de Janeiro were shot dead by a gunman.
The wounded student who took shelter in her house could not speak.
Sao Paulo Commander of Police Forces Marcelo Salles said that the gunmen used "at least one.38 caliber pistol, along with homemade bombs and a crossbow" in an attack that was an "unspeakably brutal crime".
"It's a very sad scene, the saddest thing I've seen in my entire life".