Wednesday's shooting happened in a public school in Suzano, a suburb of Sao Paulo, Brazil's largest city.
"It's a very sad scene - the saddest thing I've seen in my entire life", said Sao Paulo Governor João Doria.
Sao Paulo state authorities say eight people have been killed in a school shooting in Brazil, including two student shooters.
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. "I opened the gate to my house, and I saw children jumping over the school's wall", she said. Five children are reportedly among the dead, as well as a school employee and a passerby. Some of them were said to be in critical condition.
Inside the school, police officials found a handgun and bottles that appeared to be Molotov cocktails, known as bottle bombs.
"My friend was stabbed in the shoulder and my other friend was shot", she said.
"I heard a lot of screaming", she said. "I only left when the police arrived", teacher Sandra Perez told O Estado de S Paulo newspaper (in Portuguese).
The public school, Raul Brasil Professor, has more than 1,600 students from elementary to high school grades, teachers gathered outside said.
Even though Brazil is one of the most violent countries in the world, it is rare to see school shootings in the South American country.
Far-right President Jair Bolsonaro made relaxing gun control a cornerstone of his campaign a year ago. Soon after being inaugurated January 1, Bolsonaro issued a decree making it easier for people wanting a gun to buy and possess one.