Horacio Pereira Nunes, a retiree whose house is next to the school, said he began hearing shots around 10 a.m.
School shootings are rare in Brazil, although the country is one of the world's most violent, with more annual homicides than any other.
"Then a lot of kids started running out, all screaming", he said.
Gun laws have been extremely strict in Brazil since 2003 when former leftist President Luiz Inacio Lula de Silva signed measures that prevented ordinary citizens from carrying guns.
United States grounds all Boeing 737 Max planes
United President Scott Kirby likes to say the average major airline will see several unexpected events each year. The Federal Aviation Administration initially said it did not believe there was any reason to ground the Max 8s.
In the 1999 attack on Columbine High School in Littleton, Colorado, two students killed 13 people.
The dead included two teachers and six students, and several other people had been hospitalized after sustaining injuries, according to Gov. Joao Doria, speaking a few blocks from the public school in Suzano, a suburb of Sao Paulo, Brazil's largest city.
The gunmen were wearing masks and killed themselves after the attack, police said. Castro's body lay near Monteiro's, with the crossbow on the ground between the pair.
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. "It is the saddest thing I have seen in my life".
Confirmed Case of Measles in Collin County
One child with measles walking through a school will pretty much infect every other susceptible person in that school. I hate reading an article about a kid dying from measles all because that child did not have his or her vaccinations.
Facebook, Instagram down for millions worldwide
More than a third of Facebook users affected by the outage reported that they were experiencing a 'total blackout'. Users were reporting the issues on Twitter and the reports were also appearing on the website Down Detector .
Cleveland Browns signing DT Sheldon Richardson
Richardson is expected to part of a defensive line rotation that features Myles Garrett , Emmanuel Ogbah and Larry Ogunjobi . Schefter says Richardson is signing a three-year deal with the Cleveland Browns when free agency opens Wednesday.
IAF on high alert, 2 Pak jets spotted over PoK
Qureshi added that the Pakistan Tehreek-i-Insaf government was ensuring that NAP is followed in "letter and spirit". Bolton that Pakistan's High Commissioner to India had returned to Delhi after consultations.