Police said in a statement: 'At least five children have been killed and 15 are in hospital, some with life threatening injuries.
Around 50 people were injured in the incident where they were admitted to the local hospital.
The guard was also hospitalized in serious condition.
A local firefighter was reported saying the majority of the victims ranged in age from one to four years old, according to Associated Press.
The guard, who was aged about 50 and named as Damião Soares dos Santos, was badly burnt and later died of his injuries.
"I had just returned from visiting the nursery".
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Police said officers went to the suspect's home and visited his relatives to try to understand the motive for the attack.
But police superintendent Renato Nunes told the website of the Hoje em Dia newspaper that the guard had had mental health problems since 2014.
Witnesses told media that the man, in his 50s, had been working as a night guard at the nursery for eight years.
"This could have been worse because the babies' room was in the hall next door. As the children were bigger a lot of them were able to escape", the mayor explained.
"We believe a security guard at the nursery set himself on fire and set fire to children in the kindergarten". There have been conflicting reports on whether he died.
I'm very sorry about this tragedy involving children in Janaúba.
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