The blaze spread Saturday to the Pedrógão Grande community, forcing residents to flee the area to escape towering flames.
Portuguese Prime Minister António Costa said schools in the municipalities of Pedrogão, Figueiró and Castanheira will be closed "for an indefinite period" and exams will be postponed.
"I express my closeness with the dear Portuguese people for the devastating fire that is affecting the forests around Pedrógão Grande, causing many deaths and injuries.
It released a statement announcing a minute of silence to be held before Portugal's first match of the Confederations Cup against Mexico on Sunday and said it will make a donation to help the victims and their families.
"We have been able to determine that the origin of the fire was caused by dry thunderstorms," José Maria Almeida Rodrigues said, according to the Portuguese state-run news agency Lusa.