Police said the man responsible for the attack in the city of Blumenau has been arrested. The local security chief, Marcio Alberto Filippi, told reporters the attacker gained access to the private school by scaling its walls.
Firefighters chief Diogo said that in addition to the four children killed, five others are under medical care.
The attack, dubbed by President Luiz Inacio Lula da Silva a "monstrosity," happened nearly a week after a 13-year-old student stabbed a teacher to death and wounded five others in a Sao Paulo school.
"A tragedy like this is unacceptable, an absurd act of hate and cowardice...an act of violence against innocent and defenceless children," Lula said in a Twitter post.
"This human figure that had nothing human - it must have come from another planet, a hate planet – had the stupidity to kill four children with an axe and injure three," said Lula during a meeting with government ministers and governors in Brasilia.
Afterwards, he asked the meeting's attendees to observe a minute of silence for the families of the victims.
A man armed with a small axe climbed over a wall into a day-care centre in the city of Blumenau in the state of Santa Catarina, and killed four children on Wednesday, police said, injuring five others in the attack.
The 25-year-old man turned himself in to police after the rampage, security chief Marcio Alberto Filippi told reporters.
Police said three boys - two aged 4 and one aged 5 - and one girl aged 7 were killed.
Four of the injured children between the ages of 3 to 5 were being treated in a hospital and were reported in stable condition, while a fifth child had minor injuries, police said.
The attack came nearly a week after a 13-year-old student stabbed a teacher to death and wounded five others in a Sao Paulo school.
'How will I get this out of my daughter's mind?' says the father of the girl who survived a school attack in Brazil
Police said three boys - two aged 4 and one aged 5 - and one girl aged 7 were killed.
Four of the injured children between the ages of 3 to 5 were being treated in a hospital and were reported in stable condition, while a fifth child had minor injuries, police said. The children are expected to be discharged from the hospital tomorrow, said Blumenau deputy mayor Maria Regina Soar.
Fearing their children might be among the victims, desperate parents rushed to the day-care centre in the city of Blumenau in the state of Santa Catarina, as police and firefighters investigated the situation.
"Thank God my daughter was not among the victims," one father told reporters. "She is fine physically but emotionally destroyed. How will I get this out of my daughter’s mind?" he added.
The attacker had a history of violence and drugs and had stabbed his stepfather in March 2021, police said.
Santa Catarina State Civil Police General Delegate Ulisses Gabriel said the attacker was arrested for "the crimes of four qualified murders and four qualified attempted murders."
Reuters