The suspects are believed to be two teenagers, who shot themselves after the rampage.
São Paulo police said two young men wearing masks entered the Raul Brasil elementary school at 9.30 am local time and fired guns while the children were on their snack break.
The assailants reportedly were former students of the school, yet the motive of the attack remains unclear.
At least 17 other people, mostly children, were also shot and taken to hospitals, in which several are in serious condition.
Speaking a few blocks from the public school in Suzano, Mr Doria said: "The school is on lockdown".
Sipa USA via AP The scene outside the Raul Brasil State School in Suzano, SP, Brazil on March 13, 2019 after a shooting that has left at least eight people dead.
Eight people have been killed in a school shooting in Brazil.
The Military Police confirmed that 10 people were dead and 10 others injured after the shooting.
"I was shocked with the scenes I saw inside that school", Doria said.
A homemade video taken during the shooting and aired by Globo TV showed children screaming, running and begging for their lives as loud shots were heard.
Students gathered outside the school recounted harrowing attacks and seeing several bodies lying in pools of blood.
Security cameras from homes near the school showed children climbing and jumping over a wall that surrounds the Raul Brasil building, and sprinting down streets, screaming for help.
Latin America's most populous nation has the largest number of annual homicides in the world, but school shootings are rare.
Five students, a teacher, and an administrator at the school were killed, said Joao Camilo Pires de Campos, the state's public secretary.
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. "It is the saddest thing I have seen in my life".
- Verizon to launch mobile 5G in Chicago and Minneapolis on April 11
- With Arab Nationalities Among 157 Victims of Ethiopian Airlines Crash
- Nancy Pelosi says impeaching Donald Trump 'just not worth it'
- Compromise seeks to limit president's emergency declarations
- Jacket belonging to missing backpacker Catherine Shaw found in Guatemala
- How safe is Boeing's 737 MAX 8 aircraft? | US & Canada
- California governor places moratorium on executions
- Facebook and Instagram down in the UAE and elsewhere in the world
- North Korea Refuses to Hold WHO Regional Session Due to Sanctions
- 'Best putting round ever' lifts Molinari to brink of Bay Hill win