Authorities identified the shooters as Luiz Henrique de Castro, 25, and Guilherme Taucci Monteiro, 17.
The police reported that another shooting incident occurred near the Raul Brasil elementary school a little while before the attack at the school.
A man comforts a woman at the Raul Brasil State School in Suzano, Brazil, on Wednesday.
"I live next door, I heard a commotion and I went there..."
Horacio Pereira Nunes, whose house is next to the school, said he began hearing shots around 10am.
Police say they shot at students in a gym and fired at others who were enjoying a snack break.
The names and identities of the victims and the attacks have yet to be released and the motive for the attack is not clear. More than 1,000 children aged between 11 and 15 attend classes there.
After shooting at students in the yard, the attackers headed to the language centre where several pupils were hiding and "committed suicide in a corridor", Sales said.
Police work at the scene of a shooting at a school in Suzano, Sao Paulo metropolitan region, Brazil, on March 13, 2019.
Latin America's largest nation has the largest number of annual homicides in the world, but school shootings are rare.
According to reports, five children and two adults have been killed in a school shooting in Sao Paulo, Brazil.
However, current Brazilian President Jair Bolsonaro signed a temporary decree in January that made it easier for citizens to buy guns in an effort to overturn the strict regulations of the past.
Security camera footage from the school's entrance published on the website of O Globo newspaper showed Monteiro entering the school around 9:30 a.m.
She managed to escape, and students frantically scrambled out of the school. One student was shot in the back and another had suffered injuries to a knee.
"We can't let those who take advantage of this tragedy speak about how disarmament is the solution", he tweeted, adding: "Weak and shameful 'disarmament farce, ' which gave guns to criminals and prevented self-defense". "I put my cell phone into his hand and he typed, with his dirty hands trembling, that he wanted me to call his mom", Gonçalves said.
Salles said the gunmen used at least one.38 caliber pistol, along with homemade bombs and a crossbow.
"The teenagers were brutally murdered", São Paulo state governor João Doria said after visiting the school.